a numerical study of the mediterranean sea circulation abstract a primitive equation ocean model that makes use of a curvilinear orthogonal grid and a sigma coordinate system was used to simulate the mediterranean sea the model was forced with monthly climatological values of wind stress heat and salinity flux with the help of the curvilinear horizontal grid the larger scales of the entire mediterranean sea are modeled and the topography around the narrow and shallow straits of gibraltar is also reasonably well represented the resulting model inflow and outflow seems to mimic the real mediterranean often in considerable detail levantine intermediate water is formed in the levantine basin and exits through the strait of sicily and the strait of gibraltar deep water formation processes are clearly represented by the model the model results indicate that in the western mediterranean the wind stress is very important in establishing the summer northward shift of the atlantic inflow lateral boundary runoff surface salinity and heat fluxes are necessar

making coulomb angle oriented shear bands in numerical tectonic models abstract localization of shear strain can be induced by strain weakening plasticity in continuum models and is often used to represent faults of various scales the orientation of the shear bands is thus required to be consistent with those observed from natural faults and with simple theories of brittle failure although the coulomb angle at which a shear band satisfies the coulomb failure criterion is widely used as an assumed fault orientation the currently available numerical techniques do not always produce shear bands oriented at this angle we demonstrate that under an associated plastic flow rule for which dilation and friction angles are equal the coulomb angle becomes a unique initial shear band orientation regardless of the numerical methods employed and model resolution the known problem of overly expanding shear bands in case of a constant dilation angle is preventable if dilation angle is reduced as shear strain along the shear band increases this treatment corresponds to natural processes reducing roughness of a fault plane

exxon global cycle chart an event for every occasion the basic premise of the recent exxon cycle chart that there exists a globally correlatable suite of third order eustatic cycles remains unproven many of the tests of this premise are based on circular reasoning the implied precision of the exxon global cycle chart is not supportable because it is greater than that of the best available chronostratigraphic techniques such as those used to construct the global standard time scale correlations of new stratigraphic sections with the exxon chart will almost always succeed because there are so many exxon sequence boundary events from which to choose this is demonstrated by the use of four synthetic sections constructed from tables of random numbers a minimum of 77 successful correlations of random events with the exxon chart was achieved the existing cycle chart represents an amalgam of regional and local tectonic events and probably also includes unrecognized miscorrelations it is of questionable value as an independent standard of geologic time

numerical simulation of internal kelvin waves and coastal upwelling fronts two three dimensional primitive equation numerical ocean models are applied to the problem of internal kelvin waves and coastal upwelling in the great lakes one is the princeton ocean model pom with a terrain following sigma vertical coordinate and the other is the dietrich center for air sea technology diecast model with constant z level coordinates the sigma coordinate system is particularly convenient for simulating coastal upwelling while the z level system might be better for representing abrupt topographic changes the models are first tested with a stratified idealized circular lake 100 km in diameter and 100 m deep two bottom topographies are considered a flat bottom and a parabolic depth profile three rectilinear horizontal grids are used 5 2 5 and 1 25 km the pom was used with 13 vertical levels while the diecast model was tested with both 13 and 29 vertical levels the models are driven with an impulsive wind stress imitating the passage of a weather system in the case of the flat bottom basin the dynamical response to light wind forcing is a small amplitude internal kelvin wave for both models the speed of the kelvin wave in the model is somewhat less than the inviscid analytic solution wave speed in the case of strong wind forcing the thermocline breaks the surface full upwelling and a strong surface thermal front appears after the wind ceases the edges of this thermal front propagate cyclonically around the lake quite similar to an internal kelvin wave in the case of parabolic bathymetry kelvin wave and thermal front propagation is modified by interaction with a topographic wave and a geostrophic circulation in both models higher horizontal resolution gives higher wave and frontal speeds horizontal resolution is much more critical in the full upwelling case than in the kelvin wave case vertical resolution is not as critical the models are also applied to lake michigan to determine the response to strong northerly winds causing upwelling along the eastern shore the results are more complex than for the circular basin but clearly show the characteristics of cyclonically propagating thermal fronts the resulting northward warm front propagation along the eastern shore compares favorably with observations of temperature fluctuations at municipal water intakes after a storm although the model frontal speed was less than the observed speed

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

mantle temperature as a control on the time scale of thermal evolution of extensional basins abstract extension of the lithosphere the thermo mechanical boundary layer above the convecting mantle is followed by cooling and subsidence the timescale of oceanic basin subsidence is 100 myr whereas basins of the continental interior often subside continuously for more than 200 myr after rifting using numerical modelling we show how these diverse rifting scenarios are unified when accounting for varying mantle potential temperature at a temperature of 1300 c cooling is plate like with nearly exponential subsidence as observed in oceanic basins at 1200 c subsidence is almost linear and continues for more than 800 myr the longevity of basin subsidence in the continental interior can therefore be explained by variation of mantle temperature an additional cause of the longevity of subsidence is related to the equilibrium thickness of the lithosphere which is increased by the local reduction of heat producing elements due to crustal thinning consequently the thermally mature lithosphere of an extensional basin can be thicker than the surrounding lithosphere this mechanism contributes to additional thermal subsidence compared to the case where the base of the lithosphere is assumed held at a constant depth

orbital modulation of the earth s magnetic field intensity more than 20 years ago on the basis of data from a pacific sediment core it was suggested that geomagnetic field intensity may vary with the earth s orbital obliquity centred on a period of 41 kyr as a result of the effect of obliquity on precessional forces in the earth s core1 it had also been proposed that precession plays an important role in the energy budget of the earth s geodynamo2 but subsequent analyses indicated that the energy available from precession is at least an order of magnitude less than that required to drive the geodynamo3 here however we report a spectral analysis of sedimentary records of relative geomagnetic palaeointensity from two north atlantic sites which shows significant power both at orbital eccentricity 100 kyr and obliquity 41 kyr the eccentricity power is also present in bulk magnetic properties such as susceptibility and is therefore attributable to lithological variations controlled by eccentricity driven climate change the obliquity power however is not apparent in bulk magnetic properties and seems to be a property of the geomagnetic field itself thus providing evidence for the orbital forcing of geomagnetic field intensity

on the net cyclonic circulation in large stratified lakes schwab et al have investigated a possible cause of long term cyclonic circulation often observed in stratified lakes they conclude that the adiabatic boundary condition applied to the bottom boundary leads to cyclonic circulation in this note the authors emphasize that it is the combination of vertical mixing of density the associated bottom and surface boundary conditions and variable bottom topography that is important the authors demonstrate the mechanism using a numerical model results also demonstrate the important role of the cross shore flow driven by vertical mixing of momentum in setting the maximum azimuthal flow speed and the cross shore structure of the azimuthal flow

an adaptive staggered grid finite difference method for modeling geodynamic stokes flows with strongly variable viscosity 1 here we describe a new staggered grid formulation for discretizing incompressible stokes flow which has been specifically designed for use on adaptive quadtree type meshes the key to our new adaptive staggered grid asg stencil is in the form of the stress conservative finite difference constraints which are enforced at the hanging velocity nodes between resolution transitions within the mesh the new asg discretization maintains a compact stencil thus preserving the sparsity within the matrix which both minimizes the computational cost and enables the discrete system to be efficiently solved via sparse direct factorizations or iterative methods we demonstrate numerically that the asg stencil 1 is stable and does not produce spurious pressure oscillations across regions of grid refinement which intersect discontinuous viscosity structures and 2 possesses the same order of accuracy as the classical nonadaptive staggered grid discretization several pragmatic error indicators that are used to drive adaptivity are introduced in order to demonstrate the superior performance of the asg stencil over traditional nonadaptive grid approaches furthermore to demonstrate the potential of this new methodology we present geodynamic examples of both lithospheric and planetary scales models

surface river plume in a large lake under wind forcing observations and laboratory experiments abstract observations of a small riverine plume grand river on in the nearshore zones of lake erie were analyzed to describe its spatial variability and its thickness under different wind forcing conditions during late spring of 2012 observational results reveal a well marked frontal region in the vicinity of the river mouth causing the plume to discharge into the lake in the surface layers positive buoyant wind driven alongshore currents at the mid depth had speeds of 2 9 cm s in comparison to those in the cross shore 3 6 cm s which transported the plume along the shore during the measurement period series of laboratory experiments were conducted to obtain the propagation speed u of the buoyant plume in terms of buoyancy anomaly ba richardson number ri dimensionless time t and aspect ratio a based on our experiments we developed two non dimensional relationships describing the speed of propagation u as u ba 1 2 8 ri 1 2 t 1 3 a and the plume thickness h as h h 0 8 ri 1 4 t 1 2 a in the water depth h which are in agreement with field observations

eduction extension and exhumation of ultrahigh pressure rocks in metamorphic core complexes due to subduction initiation the controversy over the exhumation of ultrahigh pressure uhp rocks centers on whether it involves rising of pieces of crust detached from subducted continental lithosphere or an entire subducted plate that undergoes eduction i e reverse subduction we present a new thermomechanical model of continental subduction showing that these apparently contrasting mechanisms can occur together crust subducted deep enough is heated and weakened causing limited diapiric rise while crust subducted to shallower depths retains strength and is exhumed only by eduction the model also shows for the first time how eduction followed by seafloor spreading can occur in a zone of regional convergence this occurs spontaneously when subduction of buoyant crust causes a subduction zone to lock up in one place causing a new subduction zone to form in another the model is consistent with many features of the youngest region of uhp rock exhumation on earth the d entrecasteaux islands uhp exhumation and the amount of regional extension as well as the seismic structure around the islands can be explained by eduction ductile flow fabrics seen on the islands would result from exhumation of the most deeply subducted crust heated enough to undergo partial melting reversal of motion on the north dipping continental subduction zone required by this model was likely triggered by initiation of the new britain trench as suggested previously our model implies that the crust of goodenough basin south of the islands was exhumed by eduction in the last 5 ma and this hypothesis can be tested by drilling

the distinction between geomagnetic excursions and reversals summary two recent studies of the geomagnetic eld in the last 1 myr have found 14 excursions large changes in direction lasting 5 10 kyr each six of which are established as global phenomena by correlation between diierent sites the older picture of the geomagnetic eld enjoying long periods of stable polarity may not therefore be correct instead the eld appears to suier many dramatic changes in direction and concomitant reduction in intensity for 10 20 per cent of the time during excursions the eld may reverse in the liquid outer core which has timescales of 500 yr or less but not in the solid inner core where the eld must change by diiusion with a timescale of 3 kyr this timescale is consistent with the remarkably uniform duration of well dated excursions the disparity of dynamical timescales between the inner and outer cores a factor of 10 is consistent with the 10 excursions between full reversals

geodynamics layer cake or plum pudding whether convection in the earth s mantle extends through its entire depth or if the mantle is layered has long been debated recent research suggests that spatially and temporally intermittent or partial layering is the most likely solution

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

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 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

comparison of modern and geological observations of dynamic support from mantle convection the topographies of africa and antarctica form patterns of interlocking swells the relationship between topography and gravity indicates that these swells are dynamically supported by mantle convection with swell diameters of 1850 450 km and full heights between 800 and 1800 m the implication is that mantle convection not only supports swells surrounding hotspots but also influences topography across the entire surface areas of africa and antarctica we investigate whether dynamically supported swells are also observed throughout the geological record focusing on intensively studied mesozoic cenozoic sedimentary rocks around britain and ireland vertical motions of britain and ireland a typical piece of continental lithosphere far from a destructive plate boundary have been demonstrably affected by dynamic support for over half of the past 200 ma period the diameters and maximum heights of the mesozoic british swells and the modern african and antarctic swells are similar the ancient british swells grew in 5 10 ma and decayed over 20 30 ma suggesting vertical motion rates comparable with those estimated from geomorphological studies of africa igneous production rate and swell height are not correlated in the modern and the geological records mantle convection should be considered as a common control on regional sea level

why intracontinental basins subside longer 3 d feedback effects of lithospheric cooling and sedimentation on the flexural strength of the lithosphere

sedimentary basins feeling the heat from below sea level changes through earth s history have profoundly affected the surface environment resulting in alternating advances and retreats of the sea called transgressions and regressions an understanding of the mechanisms behind these major shifts in coastlines and the associated patterns of sediment deposition and erosion over different time scales is central to unraveling earth s tectonic and climate history on page 827 of this issue petersen et al 1 report results from geodynamic modeling that give a potentially radical shift in concept namely that oscillations in sedimentary sequences over time periods from 2 to 20 million years may be driven by regional patterns of small scale convection in the mantle

global changes in intensity of the earth s magnetic field during the past 800kyr recent advances in palaeomagnetic and dating techniques have led to increasingly precise records of the relative intensity of the earth s past magnetic field at numerous field sites the compilation and analysis of these records can provide important constraints on changes in global magnetic field intensity and therefore on the earth s geodynamo itself a previous compilation for the past 200 kyr integrated 17 marine records into a composite curve1 with the geomagnetic origin of the signal supported by an independent analysis of 10be production made on different cores2 the persistence of long term features in the earth s magnetic intensity or the existence of long term periodic changes cannot however be resolved in this relatively short time span here we present the integration of 33 records of relative palaeointensity3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 into a composite curve spanning the past 800 kyr we find that the intensity of the earth s dipole field has experienced large amplitude variations over this time period with pronounced intensity minima coinciding with known excursions in field direction reflecting the emergence of non dipole components no stable periodicity was found in our composite record and therefore our data set does not support the hypothesis that the earth s orbital parameters have a direct and strong influence on the geodynamo

cross shelf thermal variability in southern lake michigan during the stratified periods 1 results from a field experiment in southern lake michigan are used to quantify the cross shelf nearshore variability in great lakes temperatures during the stratified season the experiment was conducted along the indiana coast of southern lake michigan with temperature and velocity moorings arranged in a cross shelf transect that extended to approximately 20 km from shore 40 m depth the field site is noteworthy because of its location at the end of a major axis of an elliptical great lake the relatively mild bathymetric slope and local shoreline orientation that is perpendicular relative to the dominant summer winds measurements demonstrate that the location of the thermocline bottom intersection is highly variable causing a wide zone of extreme thermal variability in the nearshore region with time scales of variability ranging from hours to months near inertial internal poincare waves are shown to cause large thermocline excursions but primarily only during periods of elevated activity several full upwelling events were observed but in general they were brief lasting only 1 2 days and had very limited spatial extent 2 5 km or less nonetheless the offshore extent of the upwelling front was shown to be reasonably estimated with a simple estimate of the cross shelf transport caused by alongshore wind events a persistent feature that determined the zone of elevated thermal variability the thermocline shelf intersection point was the strongly tilted thermocline which resulted in the thermocline being located very close to shore no evidence was found to support the hypothesis that internal kelvin waves affect thermal variability at the study location

rayleigh wave tomography of china and adjacent regions 1 this paper presents a tomographic study on the s wave velocity structure of china and adjacent regions group velocity dispersions of fundamental rayleigh waves along more than 4000 paths were determined with frequency time analysis the study region was divided into a 1 1 grid and velocities in between grid nodes were calculated by bilinear interpolation the occam s inversion scheme was adopted to invert for group velocity distributions this method is robust and allows us to use a fine grid in model parameterization and thus helps to restore a more realistic velocity pattern checkerboard tests were carried out and the lateral resolution was estimated to be 4 6 in china and its eastern continental shelves the resulting group velocity maps from 10 to 184 s showed good correlation with known geological and tectonic features the pure path dispersion curves at each node were inverted for shear wave velocity structures the three dimensional velocity model indicates thick lithospheres in the yangtze and tarim platforms and hot upper mantles in baikal and western mongolia coastal area and continental shelves of eastern china and indochina and south china sea regions the tibetan plateau has a very thick crust with a low velocity zone in its middle beneath the crust a north dipping high velocity zone mimicking a subducting plate reaches to 200 km in depth and reaches to the kunlun mountains northward in northern tibet a low velocity zone immediately below the moho extends eastward then turns southward along the eastern edge of the plateau until it connects to the vast low velocity area in indochina and the south china sea

a model study of the seasonal circulation in the gulf of maine the princeton ocean model is used to study the circulation in the gulf of maine and its seasonal transition in response to wind surface heat flux river discharge and the m2 tide the model has an orthogonal curvature linear grid in the horizontal with variable spacing from 3 km nearshore to 7 km offshore and 19 levels in the vertical it is initialized and forced at the open boundary with model results from the east coast forecast system the first experiment is forced by monthly climatological wind and heat flux from the comprehensive ocean atmosphere data set discharges from the saint john penobscot kennebec and merrimack rivers are added in the second experiment the semidiurnal lunar tide m2 is included as part of the open boundary forcing in the third experiment it is found that the surface heat flux plays an important role in regulating the annual cycle of the circulation in the gulf of maine the spinup of the cyclonic circulation between april and june is likely caused by the differential heating between the interior gulf and the exterior shelf slope region from june to december the cyclonic circulation continues to strengthen but gradually shrinks in size when winter cooling erodes the stratification the cyclonic circulation penetrates deeper into the water column the circulation quickly spins down from december to february as most of the energy is consumed by bottom friction while inclusion of river discharge changes details of the circulation pattern the annual evolution of the circulation is largely unaffected on the other hand inclusion of the tide results in not only the anticyclonic circulation on georges bank but also modifications to the seasonal circulation

hydrodynamic modeling of lake ontario an intercomparison of three models 1 the solutions of three lake hydrodynamic models namely princeton ocean model pom canadian version of diecast model and estuary lake and coastal ocean model are compared with each other and with observations in lake ontario the models have the same horizontal resolution and are forced with meteorological observations during mid april to early october of 2006 the three models obtained qualitatively similar results although they have differences in physical parameters numerical scheme and vertical discretization comparison with observations shows that the models can reproduce the time evolution of lake surface temperature reasonably well all the models produced shallower mixed layers than observations at midlake stations causing significant errors in simulating the temperatures in the thermocline but performed better near the coast all the models also reproduced the characteristics of the time variability of the surface currents but quantitatively had substantial errors at subsurface levels the three models all reproduced the observed spatial pattern of the summer mean near surface temperatures with upwelling colder temperatures along the north shore and downwelling warmer temperatures along the southeastern shore the models simulated a lake wide cyclonic circulation occupying a large portion of the lake consistent with the observed climatology but showed distinct differences in simulating the smaller gyre in the western corner of the lake although pom has half vertical layers compared to z level models its performance is comparable or slightly better than other models in most of the measures during a strong easterly wind event the performances of the models are similar in simulating the upwelling and downwelling processes in the lake and agree with the expected dynamic response to the strong wind forcing

a comparison of observed and modeled surface waves in southern lake michigan and the implications for models of sediment resuspension 1 subsurface pressure sensors were used to make measurements of surface waves during 18 deployments in southern lake michigan between 1998 and 2000 most of the observations were made during the unstratified period november may in water depths between 10 and 55 m the observations as well as those obtained from the national data buoy center ndbc buoy 45007 which is located in the middle of the southern basin of the lake were compared to the results obtained from the great lakes environmental research laboratory glerl donelan wave model implemented on a 2 km grid the results show that the wave model does a good job of calculating the wave heights but consistently underestimates the wave periods in over 80 of the cases the bottom stresses calculated from both the observations and the wave model results agree as to whether or not resuspension occurs but over 70 of this agreement is for cases when resuspension does not occur both stresses predict resuspension about 6 of the time since the bottom stresses calculated from the model results are usually lower than those calculated from the observations resuspension estimates based on the wave model parameters are also lower than those calculated from the observed waves

the role of wave current interaction in lake erie s seasonal and episodic dynamics although the significance of surface gravity waves has been consistently emphasized in previous limnetic studies the roles of wave current interactions in lake dynamics are not sufficiently understood due to the lack of high resolution wave information with a two way coupled hydrodynamic and wave model system this study investigated how the lake erie dynamics are impacted by the wave induced surface and radiation stresses on the seasonal mean and episodic scales the results showed that the surface radiation stress was the same as or an order of magnitude larger than the wave induced surface stress in the nearshore area 5 km offshore while the latter prevailed in the offshore areas by enhancing air lake momentum and heat transfers the wave enhanced surface stress improved the model s skill in simulating hydrodynamics in the central and eastern basins and it was of greater importance at least an order of magnitude larger in modifying surges offshore currents and thermal structures compared to those of the radiation stress nevertheless the radiation stress played key roles in wave induced nearshore currents especially in the shallow western basin their significances reached o 0 01 to 0 1 m s on the seasonal and episodic scales respectively and could have similar importance in other shallow water environments

rheology of the upper mantle a synthesis rheological properties of the upper mantle of the earth play an important role in the dynamics of the lithosphere and asthenosphere however such fundamental issues as the dominant mechanisms of flow have not been well resolved a synthesis of laboratory studies and geophysical and geological observations shows that transitions between diffusion and dislocation creep likely occur in the earth s upper mantle the hot and shallow upper mantle flows by dislocation creep whereas cold and shallow or deep upper mantle may flow by diffusion creep when the stress increases grain size is reduced and the upper mantle near the transition between these two regimes is weakened consequently deformation is localized and the upper mantle is decoupled mechanically near these depths

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

cenozoic uplift of south western australia as constrained by river profiles abstract the relative tectonic quiescence of the australian continent during the cenozoic makes it an excellent natural laboratory to study recent large scale variations in surface topography and processes that influence changes in its elevation embedded within this topography is a fluvial network that is sensitive to variations in horizontal and vertical motions the notion that a river acts as a tape recorder for vertical perturbations suggests that changes in spatial and temporal characteristics of surface uplift can be deduced through the analysis of longitudinal river profiles we analyse 20 longitudinal river profiles around the australian continent concave upward profiles in northeast australia indicate an absence of recent surface uplift in contrast the major knickzones within longitudinal profiles of rivers in southwest australia suggest recent surface uplift given the lack of recent large scale tectonic activity in that region this uplift requires an explanation applying an inverse algorithm to river profiles of south western australia reveals that this surface uplift started in the eocene and culminated in the mid late neogene the surface uplift rates deduced from this river profile analysis generally agree with independent geological observations including preserved shallow marine sediment outcrops across the eucla basin and south western australia we show that the interplay between global sea level and long wavelength dynamic topography associated with south western australia s plate motion path over the remnants of an ancient pacific slab is a plausible mechanism driving this surface uplift

asymmetrical saw tooth pattern of the geomagnetic field intensity from equatorial sediments in the pacific and indian oceans abstract a record of relative paleointensity from marine sediments in the equatorial indian ocean spanning the last 4 ma completes a previous dataset from ocean drilling program odp leg 138 sites in the equatorial pacific 1 the timescale was defined with a precision better than 20 kyr with different and independent methods most of the features present in the record from the equatorial pacific are confirmed the overall saw tooth pattern is observed across every field reversal and the short term fluctuations superimposed on the slow intensity decrease preceding the reversals appear to be similar at both sites the global character of these features reinforces their interpretation in terms of changes in dipole field intensity and provides new important constraints on models of the geodynamo a synthetic curve of field intensity changes during the last 4 ma is proposed as a first paleointensity timescale for future stratigraphic studies

modeling summer circulation and thermal structure of lake erie athree dimensionalprimitiveequationnumericalmodelwasappliedtolakeerieona2kmgridtostudyitssummercirculation andthermalstructure modelresultswerecomparedtolong termobservationsofcurrentsandtemperaturemadein2005at severallocations mostlyinitscentralbasin intheshallowandmostlyunstrati edwesternbasincirculationisdrivenbydetroitriverin ow modi edtosomeextentbywind andisfromwesttoeast inthecentralbasin which isofintermediate depthandhasarelatively atbottom themodeledcirculationisanticyclonic clockwise drivenbyanticyclonicvorticityinthesurfacewind andthethermocline isbowl shaped inlinewithobservations inthedeeppartoftheeastern basin the thermoclineisdome shapedandcirculationiscyclonic counter clockwise duetodensitygradients acon gurationtypicalforotherlargedeeplakes whileshallower areasareoccupiedbyanticyclonic circulationdrivenbyanticyclonic windvorticity inthe centralbasin modeledtemperatureandcirculationpatternsare quitesensitivetothespeci cationofthe wind eld anticyclonicwindvorticityleadstothinningofthehypolimnion inthecentralbasinandearlierdestrati cationinthefall

a sub crustal piercing point for north atlantic reconstructions and tectonic implications plate tectonic reconstructions are usually constrained by the correlation of lineaments of surface geology and crustal structures this procedure is however largely dependent on and complicated by assumptions on crustal structure and thinning and the identification of the continent ocean transition we identify two geophysically and geometrically similar upper mantle structures in the north atlantic and suggest that these represent remnants of the same caledonian collision event the identification of this structural lineament provides a sub crustal piercing point and hence a novel opportunity to tie plate tectonic reconstructions further this structure coincides with the location of some major tectonic events of the north atlantic post orogenic evolution such as the occurrence of the iceland melt anomaly and the separation of the jan mayen microcontinent we suggest that this inherited orogenic structure played a major role in the control of north atlantic tectonic processes

high frequency moderate to high amplitude sea level oscillations during the late early aptian insights into the mid aptian event galve sub basin spain abstract this paper presents a field based stratigraphic architecture research from the aptian of spain in which high frequency 7 cycles ma moderate to high amplitude 8 127 m sea level oscillations are evidenced by the repeated incision of palaeovalleys in a carbonate platform developed during the late early aptian in a rift setting global eustacy tectonic uplift and mantle dynamic topography are considered as potential mechanisms to explain the observed relative sea level record glacioeustacy is interpreted as the most reliable mechanism to drive the observed sea level oscillations however other mechanisms as oscillations of the groundwater capacity of sedimentary basins and sudden flooding of major a basin as the south atlantic rift are also considered a major cooling event is proposed to occur during the late early aptian as a response to a large scale episode of ignimbritic volcanism increased burial of organic carbon during the aptian oae 1a and a significant demise of carbonate platforms this cooling event is interpreted as the origin for glacioeustatic sea level oscillations during the mid aptian

one dimensional ocean surface layer modeling a problem and a solution abstract the first part of this paper is generic it demonstrates a problem associated with one dimensional ocean surface layer model comparisons with ocean observations unlike three dimensional simulations or the real ocean kinetic energy can inexorably build up in one dimensional simulations which artificially enhances mixing adding a sink term to the momentum equations counteracts this behavior the sink term is a surrogate for energy divergence available to three dimensional models but not to one dimensional models the remainder of the paper deals with the mellor yamada boundary layer model there exists prior evidence that the model s summertime surface temperatures are too warm due to overly shallow mixed layer depths if one adds a sink term to approximate three dimensional model behavior the warming problem is exacerbated creating added incentive to seek an appropriate model change guided by laboratory data a richardson number dependent dissipation is introduced and this simple modificat

river incision circulation and wind regime of pleistocene lake bonneville usa abstract pleistocene lake bonneville of the western u s and its associated alluvial systems present a unique opportunity to understand the relationship between prevailing winds of the time lake circulation and river incision the lake underwent a catastrophic flooding event 18 300 yr b p resulting in the incision of streams entering the lake along its eastern border incision patterns of twelve streams and rivers suggest that they were influenced by the prevailing circulation in the lake at the time in order to match patterns of river incisions simulations of lake circulation were performed with a state of the art numerical model for the maximum transgressive bonneville lake elevation simulations were conducted using the forcing of westerly and easterly prevailing winds simulated circulation can be described in terms of simple geostrophic balances in which the currents are generally cyclonic counter clockwise for westerly winds and anti cyclonic clockwise for easterly winds irregularities in lake shorelines and bathymetry cause localized variation of this general pattern comparison of model output with the deflected stream incision patterns suggest that prevailing winds during the pleistocene in the great basin of north america were westerly and that unlike the interior of north america the continental ice sheet did not exert significant influence on the climatological wind patterns of the great basin

a link between geomagnetic reversals and events and glaciations abstract the apparent duration of geomagnetic polarity events in arctic ocean sediments is much longer than in sediments from lower latitudes in fact while the remanence of brunhes age sediment cores from the yermak plateau at 82 n is fully reversed for 30 of their lengths 1 the events often evade detection in many other continuously deposited sediments for example the laschamp event is absent in an otherwise high resolution record of secular variation from lac du bouchet 2 which is located near the laschamp volcanics where the event was first detected very short event durations of a few hundred years at the most have been suggested before 2 3 because sedimentation rates in the arctic ocean were increased during glaciations the exaggerated proportion of reverse polarities in sediments from high latitudes suggests a link between glaciation and field reversals this suggestion is supported by magnetostratigraphic results obtained from thick loess paleosol sequences in china 4 these demonstrate that all polarity boundaries separating chrons and subchrons since the gauss matuyama field reversal have been recorded in loess and thus during periods of cold climate although conflicting evidence exists for some boundaries furthermore the ages of 22 events and chron boundaries have been compared with the oxygen isotope record 5 thought to represent global ice volume all events and reversals younger than 2 6 ma may have occurred during periods of global cooling or during cold stages however some ages are still too poorly dated for a definite correlation climatic signals also exist in the two longest relative paleointensity records 6 7 but these are suspected to be caused by climatically driven variations in the rock magnetic parameters a mechanism for field reversals may be the acceleration of the earth s rotation caused by lowering of the sea level during glaciations the short duration of events also implies that the geomagnetic field can reverse an order of magnitude faster than commonly assumed

rapid late pleistocene holocene uplift and coastal evolution of the southern arabian persian gulf the coastline along the southern arabian gulf between al jubail kingdom of saudi arabia and dubai uae appears to have risen at least 125 m in the last 18 000 years dating and topographic surveying of paleo dunes 43 53 ka paleo marine terraces 17 30 ka and paleo marine shorelines 3 3 5 5 ka document a rapid 1 mm a subsidence followed by a 6 mm a uplift that is decreasing with time the mechanism causing this movement remains elusive but may be related to the translation of the coastal area through the backbasin to forebulge hinge line movement of the arabian plate or alternatively by movement of the underlying infracambrian age hormuz salt in response to sea level changes associated with continental glaciation independent of the mechanism rapid and episodic uplift may impact the design of engineering projects such as nuclear power plants airports and artificial islands as well as the interpretation of sedimentation and archeology of the area

post rift influence of small scale convection on the landscape evolution at divergent continental margins abstract after decades of geological and geophysical data acquisition along with quantitative modeling of the long term evolution of the landscape at divergent continental margins the search for an explanation for the formation and evolution of steep escarpments bordering the coast is still a challenging task one difficult aspect to explain about the evolution of these escarpments is the expressive variability of denudation rate through the post rift phase observed in many margins here i propose that the interaction of small scale convection in the asthenosphere with the base of the continental lithosphere can create intermittent vertical displacements of the surface with magnitude of a few hundreds of meters at the continental margin these topographic perturbations are sufficient to produce an expressive variability in the rate of erosion of the landscape through the post rift phase similar to the exhumation history observed along old divergent margins i show that the vertical motion of the surface is amplified when a mobile belt is present at the continental margin with lithospheric mantle less viscous than the cratonic lithosphere and consequently more prone to be partially eroded by the convective asthenosphere i conclude that the influence of small scale convection is not the primary explanation for the formation of high topographic features at divergent continental margins but can be an important component contributing to sustain a preexistent escarpment the present results are based on numerical simulations that combine thermochemical convection in the mantle flexure of the lithosphere and surface processes of erosion and sedimentation

a detailed palaeointensity and inclination record from drill core soh1 on hawaii abstract a new record of absolute palaeointensity was obtained from drill core scientific observation hole 1 soh1 on kilauea volcano hawaii kilauea s high eruption rate resulted in a relatively continuous record and stratigraphic constraints preserved the chronological order three hundred and sixty samples were studied with the thellier thellier technique which gave 195 successful palaeointensity and 271 successful inclination determinations three geomagnetic excursions were observed which exhibited intensity reductions of about 50 initial age control from k ar and ar ar dating only constrained the total age between 20 and 120 ka the final age model was obtained by stretching the soh1 record relative to other hawaiian palaeomagnetic data this gave an age range of 0 45 ka for the flows and identified the excursions as the hilina pali mono lake and laschamp events the soh1 record of the hilina pali event is the most detailed ever incorporating data from around 40 flows this age model suggests that kilauea had a burst of activity at the soh1 site around 20 ka all available data was combined to form a composite record of palaeointensity and inclination on hawaii for 0 45 ka

modeling the 1998 2003 summer circulation and thermal structure in lake michigan 1 a three dimensional primitive equation numerical model was applied to lake michigan on a 2 km grid for 6 consecutive years to study interannual variability of summer circulation and thermal structure in 1998 2003 the model results were compared to long term observations of currents and temperature at seven moorings and two noaa buoys the accuracy of modeled currents improved considerably relative to previous summer circulation modeling done on a 5 km grid while the accuracy of temperature simulations remained the same particle trajectory model results were also compared with satellite tracked surface drifter observations large scale circulation patterns tend to be more cyclonic counterclockwise toward the end of summer as the thermocline deepens and density effects become more important circulation in southern lake michigan appears to be more variable than circulation in northern lake michigan an important new feature not previously seen in observations was found in southern lake michigan an anticyclonic gyre extending northward from the southern shore of lake michigan sometimes occupying the entire southern basin

the ties linking rock and fossil records and why they are important for palaeobiodiversity studies a correlation exists between the quality of the rock record and the diversity of fossils recorded from that rock record but what drives that correlation and how consistent that correlation is across different environments remain to be determined palaeontologists wishing to investigate past diversity patterns need to first address issues of geological bias in their data the fossil record provides the only empirical evidence of how life has diversified over geological time but it needs to be interpreted with caution for many years the history of diversity was estimated simply by summing up the numbers of taxa species genera families palaeontologists have recorded from successive geological time intervals or extrapolated from their first and last occurrences in the geological record this time series approach led to what is now a classic view of how diversity has changed over time sepkoski et al 1981 benton 1995 sepkoski 1997 such counts take the fossil record at face value or assume that biases or errors are randomly distributed in such a way that the overall effect is negligible we now realize that this is only a first crude approximation that may be subject to a number of strong biases that arise because of the nature of the sedimentary rock record time series analysis requires that sampling be carefully controlled for best results ideally data should be collected so that sampling from each time interval is uniform or at least sampled fairly using the shareholder quorum subsampling method alroy 2010 otherwise apparent changes in diversity may arise for spurious reasons for example because a a time intervals being sampled are of variable duration longer time intervals 1 4 more recorded diversity or b a time interval has been more intensively sampled more localities specimens habitats formations sampled 1 4 more recorded diversity while for a biological survey it is easy to plan a sampling strategy that will give approximately equal effort and coverage for observations palaeontologists are faced with a much more difficult task firstly the time bins they work with are irregular and highly variable in their duration for example the durations of one of the most widely used time scales has intervals spanning two orders of magnitude gradstein et al 2004 secondly and much more critically palaeontologists are collecting from an already incomplete and highly biased set of rocks which in turn skew the range of taxa and habitats that can be sampled zuschin et al 2011 bluntly put we cannot sample what is not preserved in the rock record although phylogenetic and molecular approaches can attempt to compensate pol norrell 2006 bininda emonds et al 2007 wills 2007 o connor et al 2011 so while it may be possible to standardize for sampling effort from the rock record that remains those rocks might provide a far from uniform sample of the sediments and palaeoenvironments that were originally present palaeontologists cannot therefore assume uniform sampling of the fossil record and must try to assess how the rock record they have to work with has affected their ability to sample evenly and then develop methods that compensate appropriately for this variation in recent years therefore palaeobiodiversity studies have become more probabilistic in their approach concerned with establishing confidence limits around estimates that try to correct for uneven sampling alroy et al 2001 2008 and testing empirical patterns against model predictions foote 2001 smith mcgowan 2007 mcgowan smith 2008 if we are to improve our estimates of biodiversity over time then sampling parameters need to be better quantified and we need to better understand the complex interrelationship between rock and fossil records this is no simple task and requires a more systematic approach to recording culture as well as better documentation of the variables benton et al 2011 figure 1 summarizes the problem as we see it palaeontologists estimate past diversity from remains preserved in the rock record as with any from mcgowan a j smith a b eds comparing the geological and fossil records implications for biodiversity studies geological society london special publications 358 1 7 doi 10 1144 sp358 1 0305 8719 11 15 00 the geological society of london 2011 biological survey variation of sampling effort of the surviving rock record needs to be factored out but this rock record has already passed through a geological filter that has altered and distorted not only the rock area that survives to sample but also the proportions of facies and the preservational quality of its fossil record were this geological filter to remain approximately constant over time there would be little problem of interpreting the biological signal however it is far from uniform with amounts of rock to sample proportions of facies represented by those rocks and preservation potential all varying from one time interval to the next to interpret observed changes in sampled biodiversity estimates correctly we must therefore first understand the role of the geological filter variability of the rock and fossil records

an 60 million year periodicity is common to marine 87sr 86sr fossil biodiversity and large scale sedimentation what does the periodicity reflect abstractwe find that the marine 87sr 86sr record shows a significant periodicity of m yr the 87sr 86sr record is out of phase with a 62 3 m yr periodicity previously reported in the record of marine animal diversity these periodicities are close to 58 4 m yr cycles found for the number of gap bounded sedimentary carbonate packages of north america we propose that these periodicities reflect the operation of a periodic pulse of the earth in large scale earth processes these may be linked to mantle or plate tectonic events possibly uplift which affects the earth s climate and oceans and thus the geochemistry sedimentation and biodiversity of the marine realm

integrating historical topographic maps and srtm data to derive the bathymetry of a tropical reservoir this paper proposes a cheap and fast method for est imating the bathymetry of hydroelectric reservoirs brazil has more than 30 l arge hydroelectric reservoirs with volume exceeding one billion cubic meters the hydroelectric sector is responsible for 97 of energy generation being the largest hydroele ctric park in the world these dams however cause a series of environmental social an d economic impacts which need to be monitored among the variables affecting the env ironmental impact posed by reservoirs depth has a key role because it acts on the aquatic system hydrodynamics reservoir depth distribution the bathymetry is al so a fundamental factor controlling physical chemical and biological properties of the system in brazil the acquisition of bathymetric information for the large reservoirs h owever is not a simple task because 1 most of the topographic maps available in the ar ea covered by the lake have very small scale 1 100 000 and smaller 2 larger char ts are property of the hydropower companies and are classified 3 the size of the re servoirs prevent the use of bathymetric surveys due the challenge therefore is how to comb ine the use of low precision topographic charts from the period previous to rese rvoir filling srtm data to obtain a bathymetric map which could be used for planning echo bathymetric missions so as reducing both cost and time of data acquisition and processing

on a tectonic mechanism for regional sealevel variations abstract no satisfactory tectonic explanations have yet been offered for the apparent sealevel fluctuations of about 1 cm 1000 years and a magnitude of up to a few hundred meters that have been proposed by vail et al 1 we propose a mechanism that does appear to be able to explain these changes if horizontal stresses of the order of a few kilobars occur in the lithosphere and if changes in these stress fields occur on geological time scales the proposed model is one of an interaction between these stresses and the deflections of the lithosphere caused by sedimentary loading apparent sealevel changes of up to 100 m can be produced at the flanks of the sedimentary basins by this interaction the mechanism is most effective for young margins that are subject to rapid sediment loading by its nature the tectonic model can explain contemporaneous fluctuations in apparent sealevel in neighbouring depositional environments in principle it implies the possibility of regional correlations in different basinal settings

dynamic topography and long term sea level variations there is no such thing as a stable continental platform abstract globally uniform i e eustatic sea level trends with time scales approaching 100 myr have been inferred from both seismic and backstripping stratigraphic analysis at a small set of geographic sites that are presumed to lie on stable continental platforms and passive continental margins characterized by simple thermal subsidence histories e g the new jersey margin the western african margin we demonstrate using mantle flow simulations based on high resolution seismic tomography that both the new jersey margin and the conjugate western african margin have been subject to orders of 100 m of dynamic i e flow induced topography change over the last 30 myr we also show that the changing pattern of downwelling mantle flow associated with plate subduction is a significant contributor to the background eustatic sea level trend which is also of order 100 m during the 30 myr time window therefore late cenozoic variations of dynamic topography on these passive margin sites are comparable to the eustatic sea level changes and can partially mask the latter furthermore even if the observed trend could be accurately corrected for local dynamic topography variation the residual eustatic signal does not merely reflect changes in mean spreading rates at mid ocean ridges we conclude that the observed long term sea level variations at so called stable sites cannot be interpreted as eustatic moreover previous analyses that have used long term sea level trends as a proxy for spreading rates and geochemical fluxes must be revisited

normalized remanence in sediments of the western equatorial pacific relative paleointensity of the geomagnetic field piston cores from the ontong java plateau collected during the eurydice expedition have been used to estimate regional geomagnetic paleointensity rock magnetic measurements of the sediments show that 1 the remanence is carried by stable pseudo single domain magnetite 2 the grain sizes and concentrations are relatively uniform with respect to the normalization technique and 3 susceptibility is an adequate parameter for normalizing remanent intensity in order to determine relative variations in the intensity of the paleomagnetic field we therefore have measured the remanent intensity both natural and demagnetized to 15 mt and susceptibility of archive quarters of three cores at centimeter intervals using an automated through bore magnetometer a further test of the normalized intensity records is provided by the coherence function between the normalized remanence and the susceptibility of the cores one of our cores displays high coherence over a broad range of frequencies while for two others coherence is insignificantly different from zero at the 95 level of confidence oxygen isotopic records paleontological datum levels and the brunhes matuyama boundary provide an independent temporal framework for inter core comparison when the two cores which pass our acceptance criteria are placed on a common time scale the coherence between the normalized intensity records is significantly different from zero at well above the 95 level of confidence suggesting some common input signal over the same band of frequencies furthermore there is a great deal of similarity between the records from the ontong java plateau and a record from core rc10 167 taken some 3000 km to the north the distribution of intensities obtained from these sedimentary records has the same shape as the absolute virtual dipole moment data obtained from lava flows 0 5 ma with a slightly smaller standard deviation the inter core agreement within a single region the similarity of records from 3000 km apart and the general correspondence of statistical character of these sediments with lava flow data all argue that the normalized intensity records presented here reflect variations in the intensity of the ancient geomagnetic field spectral analysis of the paleointensity time series shows that there a is significant enhancement of variance concentrated in frequencies around 33 thousand years over the period 0 350 ka this feature is however lacking for the period 350 700 ka

geomagnetic paleointensity variation with a 100 kyr quasi period abstract we analyzed records of geomagnetic field intensity paleointensity during the last 700 kyr in five sediment cores from a wide region of the pacific ocean a global paleointensity variation with a 100 kyr quasi period was successfully extracted using the wavelet transform because the variation does not correlate with that of magnetic properties of the sediments it originated from a change in the geomagnetic field the 100 kyr quasi period of the geomagnetic field is close to the timescales of eccentricity one of the earth s orbital elements and of the glacial interglacial cycle of the late quaternary paleoclimate in particular there is a correlation between the variations of the geomagnetic field intensity and climate with an 18 kyr time lag while the geodynamo has widely been thought to be a self sustained system our results support the possibility of an external energy supply of the variation through orbital forcing or climate change

climate changes control offshore crustal structure at south china sea continental margin a b s t r a c t rifted continental lithosphere subsides as a consequence of combined crustal thinning and mantle lithosphere cooling yet basins on some continental margins experience anomalous subsidence events that postdate active extension deep basins on the northern margin of the south china sea notably the baiyun sag show basement subsidence accelerating after 21 ma postdating extension by several million years we combine geophysical observations and numerical forward modeling to show that loading of the offshore basins by increased sediment flux caused by faster onshore erosion following early miocene monsoon intensification is a viable trigger for ductile flow after the cessation of active extension this illustrates that offshore basin dynamics at continental margins with weak crust can be controlled by onshore surface processes in a newly recognized form of climate tectonic coupling

reducing numerical diffusion effects with pycnocline filter numerical or artificial diffusion is the unintentional smoothing of gradients associated with the discretization of the transport equations in lakes and reservoirs where through flow is small the effects of numerical diffusion of mass are cumulative leading to a progressive weakening of vertical density stratification this density field misrepresentation precludes accurate long term three dimensional 3d hydrodynamic simulations on fixed grids in closed basins with an active thermocline an ad hoc technique to limit the destratifying effects of numerical diffusion of mass is presented and tested for a 3d hydrostatic z coordinate numerical model the technique quantifies the domain integrated numerical diffusion by assessing the change in the background potential energy eb at each time step the change in eb associated with numerical diffusion is calculated then removed using a sharpening filter applied to each water column in idealized test cases the filtering technique is effective in maintaining density stratification over one year while undergoing periodic large amplitude forcing by internal waves forty day simulations of lake kinneret compared to field measurements demonstrate improved representation of density stratification using the filtering technique

reversible subsidence on the north west shelf of australia the northwest shelf nws of australia is characterized by offshore basins associated with permian and jurassic rifting and was only slowly subsiding by the neogene international ocean discovery program iodp expedition 356 targeted this region by coring four sites in the northern carnarvon and roebuck basins and two sites in the perth basin to the south on the australian western margin we use detailed lithological physical property and age data with paleobathymetric interpretations to infer tectonic subsidence apparently confined to the nws that reverses uplifts with about the same amplitude and rate as an earlier subsidence event about 300 m of tectonic subsidence occurred over one million years from 6 to 5 million years ago and then reverses when 300 m of tectonic uplift occurred from 2 to 1 ma the along strike extent of this subsidence pattern is 400 km the similarity of magnitude and duration of the subsidence and uplift phases suggest that the subsidence is reversible the results cannot be explained by glacial eustatic variability nor can the uplift event be attributed to sediments filling the accommodation space generated earlier reversible subsidence is a key fingerprint of dynamic topography although the rates of subsidence and uplift are roughly 300 m myr a substantial portion of the changes occur over less than 1 myr and the rates inferred from a detailed least squares analysis can reach up to about 500 m myr these rates are incompatible with dynamic topography associated with motion of australia over large scale convection 10 to 40 m myr or that associated with instability of the base of the lithosphere 15 m myr the vertical motions are too large to be associated with simple flexure of a plate and plate buckling in that the required amplitudes would lead to permanent deformation of the plate a new geodynamic mechanism is required to fit the observations

modeling circulation and thermal structure in lake michigan annual cycle and interannual variability a three dimensional primitive equation numerical model was applied to lake michigan for the periods 1982 1983 and 1994 1995 to study seasonal and interannual variability of lake wide circulation and thermal structure in the lake the model was able to reproduce all of the basic features of the thermal structure in lake michigan spring thermal bar full stratification deepening of the thermocline during the fall cooling and finally an overturn in the late fall large scale circulation patterns tend to be cyclonic counterclockwise with cyclonic circulation within each subbasin the largest currents and maximum cyclonic vorticity occur in the fall and winter when temperature gradients are low but wind stresses are strongest the smallest currents and minimum cyclonic vorticity occur in spring and summer when temperature gradients are strong but wind stresses are weakest all these facts are in agreement with observations the main shortcoming of the model was that it tended to predict a more diffuse thermocline than was indicated by observations and explained only up to half of the variance observed in horizontal currents at timescales shorter than a day

circulation during winter and northerly storm events in southern lake michigan 1 moored observations of winds currents and temperature made off the southeastern lake michigan shore during 1998 to 2000 winter spring periods are studied to describe the mean winter circulation and episodic circulation during northerly storms in lake michigan late winter spring sediment plumes in southeastern lake michigan were attributed to these episodic circulation features the winter spring currents in southeastern lake michigan are quite depth independent and the mean currents flow predominantly alongshore and toward the north the observed currents show the signature of a forced two gyre circulation in the southeastern basin the interannual variability of mean and fluctuating currents is mainly due to the variability of prevailing wind forcing the intermittent episodic circulation influenced by northerly storms causes significant asymmetry to the mean circulation during northerly storm episodes the mean current speeds increased significantly and the currents within 10 km of shore followed the surface wind stress while farther offshore the circulation was oppositely directed during these episodes it is also observed that the combination of directly wind forced currents and northward propagating vorticity wave generates significant offshore transport in this region

when does small scale convection begin beneath oceanic lithosphere convection on a scale smaller than the horizontal dimensions of lithospheric plates can be produced by instabilities in the upper or lower boundary layer of the larger mantle flow small scale convection associated with the upper boundary layer should pro duce a detectable gravity signal and affect the rate of cooling and subsidence of the lithosphere i describe here a numerical model of small scale convection in a fluid of variable viscosity the results indicate that recently observed gravity anomalies1 showing a pat tern of highs and lows aligned in the direction of oceanic plate motion may be the result of small scale mantle flow the convective flow must begin in the first 6 myr of lithospheric cooling to produce the observed signals which is not inconsistent with constraints on the viscosity of the mantle the calculated trend for the subsidence of the ocean floor is found to be almost linear with time 1 2 even when small scale convection has significantly changed the rate of subsidence for average shallow asthenospheric viscosities of 1018 pa s the model subsidence can match data for the oceans2 3 and reproduce the magnitude and wavelength of the observed gravity anomalies

evidence for a new geomagnetic reversal from lava flows in idaho discussion of short polarity reversals in the brunhes and late matuyama polarity chrons k ar ages and paleomagnetic data for basalt samples from a new core hole site e at the idaho national engineering laboratory inel indicate that the age of the reversed polarity event recorded in snake river plain lavas is older than 465 50 ka 1000 years before present reported previously by champion et al 1981 nine basalt flows eight with normal polarity and one with reversed polarity were recognized in the site e core hole the flows above and below the reversed flow have ages of 491 80 ka and 580 93 ka respectively the inclination of the paleomagnetic field direction of the reversed flow at site e agrees with the inclination of reversed flows elsewhere at inel which have an age of 565 14 ka these reversed flows were previously thought to be correlative with the emperor event we suggest that this polarity event is an older event which we name the big lost reversed polarity subchronozone and subchron a review of data documenting short reversal records from volcanic and sedimentary rocks shows that there is evidence for eight polarity subchrons in the brunhes and two besides the jaramillo in the late matuyama these 10 short subchrons begin to indicate the many short events that cox 1968 hypothesized must exist if polarity interval lengths have a poisson distribution these events are true subchrons not excursions and may or may not have low associated paleointensities although low field strengths might explain why the reversal process aborts the mean sustained polarity interval length since late matuyama chron time is 90 000 years the similarity of this number with the 105 year period of the earth s orbital eccentricity suggests anew that linkage between geomagnetic paleoclimatic and possible underlying earth orbital parameters should be evaluated

sequence architecture of the bighorn dolomite wyoming usa transition to the late ordovician icehouse abstract although major late ordovician glaciation was confined to the terminal ordovician hirnantian stage lasting less than 2 million years recent isotopic evidence suggests a prolonged interval of slow growth in polar ice caps tropical carbonate platforms from passive margins and epicontinental seas offer the opportunity to monitor changes in eustatic sea level changes that accompanied this transition from a greenhouse towards an icehouse climate the late ordovician bighorn dolomite of northern wyoming and adjacent states preserves such a transition the bighorn dolomite was deposited on a northeastward facing subequatorial platform and it consists of three third order depositional sequences each is bounded by a regional erosional surface commonly with erosional truncation visible at outcrop scale and commonly mantled by a distinctive brecciated horizon the bighorn dolomite is dominated by highly bioturbated and fossiliferous open marine shallow subtidal facies but portions also contain dolomitic bioturbated restricted marine shallow subtidal and laminated peritidal facies as well as thin bedded argillaceous and fossiliferous deep subtidal limestone the three depositional sequences preserve a transition in their internal cyclicity that is consistent with computer modeling of the stratigraphic signal of increasing period and amplitude of eustatic sea level changes the lowermost sequence which spans the lander and steamboat point members consists of homogeneous acyclic shallow subtidal facies with a few meter scale peritidal parasequences near its top the middle sequence which corresponds to the leigh member contains acyclic to weakly cyclic restricted shallow subtidal and peritidal facies the uppermost sequence consisting of the horseshoe mountain member is dominated by five decameter scale parasequences composed of open marine shallow subtidal restricted shallow subtidal and peritidal facies overall the bighorn dolomite is interpreted to represent deposition during a shift from low amplitude a few meters short period 20 kyr cyclicity to moderate amplitude 10 m long period 100 kyr cyclicity indicating a shift from greenhouse conditions towards icehouse conditions a shift that agrees with recent isotopic evidence for changing late ordovician climate

review short term sea level changes in a greenhouse world a view from the cretaceous abstract this review provides a synopsis of ongoing research and our understanding of the fundamentals of sea level change today and in the geologic record especially as illustrated by conditions and processes during the cretaceous greenhouse climate episode we give an overview of the state of the art of our understanding on eustatic global versus relative regional sea level as well as long term versus short term fluctuations and their drivers in the context of the focus of unesco iugs igcp project 609 on cretaceous eustatic short term sea level and climate changes we evaluate the possible evidence for glacio eustasy versus alternative or additional mechanisms for continental water storage and release for the cretaceous greenhouse and hothouse phases during which the presence of larger continental ice shields is considered unlikely increasing evidence in the literature suggests a correlation between long period orbital cycles and depositional cycles that reflect sea level fluctuations implying a globally synchronized forcing of eustatic sea level fourth order depositional sequences seem to be related to a 405 ka periodicity which most likely represents long period orbital eccentricity control on sea level and depositional cycles third order cyclicity expressed as time synchronous sea level falls of 20 to 110 m on 0 5 to 3 0 ma timescales in the cretaceous are increasingly recognized as connected to climate cycles triggered by long term astronomical cycles that have periodicity ranging from 1 0 to 2 4 ma future perspectives of research on greenhouse sea level changes comprise a high precision time scale for sequence stratigraphy and eustatic sea level changes and high resolution marine to non marine stratigraphic correlation

on the lehmann discontinuity the lehmann discontinuity 200km in the upper mantle is proposed to result from a change in the preferred orientation of olivine as a result of a change in deformation mechanism in the shallow upper mantle deformation is due to dislocation creep and results in an anisotropic structure whereas in the deeper upper mantle diffusion creep becomes dominant due to a smaller activation volume resulting in an isotropic structure for anisotropy due to dislocation glide corresponding to a horizontal flow the resultant anisotropy will yield vsh vsv and vph vpv thus for waves propagating nearly vertically e g scs waves there will be discontinuous jumps in the s and p wave velocities at this discontinuity in this model the depth of the lehmann discontinuity depends on the deformation conditions such as stress level geotherm water fugacity and grain size giving a natural explanation for its observed variation with tectonic setting

wilson cycle passive margins control of orogenic inheritance on continental breakup abstract rifts and passive margins often develop along old suture zones where colliding continents merged during earlier phases of the wilson cycle for example the north atlantic formed after continental break up along sutures formed during the caledonian and variscan orogenies even though such tectonic inheritance is generally appreciated causative physical mechanisms that affect the localization and evolution of rifts and passive margins are not well understood we use thermo mechanical modeling to assess the role of orogenic structures during rifting and continental breakup such inherited structures include 1 thickened crust 2 eclogitized oceanic crust emplaced in the mantle lithosphere and 3 mantle wedge of hydrated peridotite serpentinite our models indicate that the presence of inherited structures not only defines the location of rifting upon extension but also imposes a control on their structural and magmatic evolution for example rifts developing in thin initial crust can preserve large amounts of orogenic serpentinite this facilitates rapid continental breakup exhumation of hydrated mantle prior to the onset of magmatism on the contrary rifts in thicker crust develop more focused thinning in the mantle lithosphere rather than in the crust and continental breakup is therefore preceded by magmatism this implies that whether passive margins become magma poor or magma rich respectively is a function of pre rift orogenic properties the models show that structures of orogenic eclogite and hydrated mantle are partially preserved during rifting and are emplaced either at the base of the thinned crust or within the lithospheric mantle as dipping structures the former provides an alternative interpretation of numerous observations of lower crustal bodies which are often regarded as igneous bodies the latter is consistent with dipping sub moho reflectors often observed in passive margins

source of tiny wiggles in chron c5 a comparison of sedimentary relative intensity and marine magnetic anomalies 1 in addition to the well established pattern of polarity reversals short wavelength fluctuations are often present in both sea surface data tiny wiggles and near bottom anomaly data while a high degree of correlation between different geographical regions suggests a geomagnetic origin for some of these wiggles anomaly data alone cannot uniquely determine whether they represent short reversals or paleointensity variations independent evidence from another geomagnetic recording medium such as deep sea sediments is required to determine the true nature of the tiny wiggles we present such independent evidence in the form of sedimentary relative paleointensity from chron c5 we make the first comparison between a sedimentary relative paleointensity record odp site 887 at 54 n 148 w and deep tow marine magnetic anomaly data 43 n 131 w bowers et al 2001 for chron c5 the sediment cores are densely sampled at 2 5 kyr resolution the inclination record shows no evidence for reverse intervals within the 1 myr long normal chron c5n 2n rock magnetic measurements suggest that the primary magnetic carrier is pseudo single domain magnetite we choose a partial anhysteretic magnetization parm as our preferred normalizer and the resulting relative paleointensity record is used as input to a forward model of crustal magnetization we then compare the results of this model with the stacked deep tow anomaly records the two records show a significant degree of correlation suggesting that the tiny wiggles in the marine magnetic anomalies are likely produced by paleointensity variations an analysis of our sampling density suggests that if any reverse intervals exist at this site they are likely to be 5 kyr in duration furthermore we suggest that reverse intervals during chron c5n 2n documented in other locations are unlikely to be global

excursions in geomagnetism the intensity of earth s magnetic field varies on timescales varying from seconds to tens of millions of years only with palaeomagnetic records going back deep into the past can putative causes for the variations be tested a new composite analysis of 33 records covers the past 800 000 years one conclusion to be drawn for it is that it seems unlikely that field intensity has been influenced by variations in earth s orbit

application of stratigraphic frameworks and thermochronological data on the mesozoic sw gondwana intraplate environment to retrieve the parana etendeka plume movement abstract since plate tectonics has been linked to material flow in the earth s mantle it is commonly accepted that convective motion in the sublithospheric mantle results in vertical deflections and horizontal plate motion on the earths surface those mantle flow driven vertical deflections are recognized through significant signals and traces in the sedimentary records unconformities and missing sections recently friedrich et al 2018 introduced an event based plume stratigraphic framework that uses such signals in the stratigraphic record to detect the geological evolution near and on the earth s surface in areas of interregional scale caused by mantle plume movement information about these dynamic processes is stored in geological archives such as 1 stratigraphic records of sedimentary basins and 2 thermochronological data sets of igneous metamorphic and sedimentary rocks for the first time this research combines these two geological archives and applies them to the mesozoic sw gondwana intraplate environment to retrieve the parana etendeka plume movement prior to the parana etendeka lip we compiled 18 stratigraphic records of the major continental and marine sedimentary basins and over 35 thermochronological data sets including 1300 apatite fission track ages surrounding the parana etendeka large igneous province to test the event based plume stratigraphic framework and its plume stratigraphic mapping to retrieve the timing and spatial distribution of the parana etendeka plume the plume stratigraphic mapping using the stratigraphic records is suitable to demark a possible plume center plume margins and distal regions friedrich et al 2018 thermochronological data reveal centers of a significant thermal parana etendeka plume influence both archives show significant signals and traces of mantle plume movement well in advance of the flood basalt eruptions our ltt data combined with stratigraphic records are modeled successfully with respect to a viable mantle plume driven thermal evolution and therefore we suggest that thermochronological data in combination with stratigraphy records have the potential to retrieve the parana etendeka plume movement

saw toothed variations of relative paleointensity and cumulative viscous remanence testing the records and the model a recent model kok and tauxe 1996a that attempts to explain asymmetrical sawtooth patterns of relative paleointensity from sediments valet and meynadier 1993 as the consequence of cumulative long term viscosity effects has been tested theoretically and experimentally a mathematical description of the model demonstrates that only a sharp distribution of relaxation times would be able to match the paleomagnetic record which implies that all the magnetic grains would be identical this has direct consequences for the distribution of the blocking temperatures tb which would not exceed 260 c and for the coercivities of the natural remanent magnetization nrm this tb spectrum derived from the model is inconsistent with the unblocking temperatures of the nrm and with the tb spectrum of the experimental thermoremanent magnetization trm of the sediment that recorded the sawtooth new results including thermal demagnetization and thellier thellier experiments across brunhes matuyama confirm the overall stability of the original records the stability of the older part of the record 2 to 4 ma has also been strengthed the sawtooth is unchanged between 20 mt and 65 mt and thermal demagnetization in a neutral atmosphere at 300 c and 450 c duplicates the results obtained by alternation field a f demagnetization thus viscous processes at least within the framework of a cumulative viscous model and for the existing data sets are not responsible for saw toothed paleointensity records

solute dispersion in the coastal boundary layer of southern lake michigan 1 we evaluate a three dimensional nested grid nearshore model of lake michigan for its ability to describe key aspects of hydrodynamics and solute transport using data from a field study conducted in summer 2008 velocity comparisons with observations from five bottom mounted adcps at different depths in the coastal boundary layer cbl show that the numerical model was able to simulate currents and flow reversals accurately within the inertial boundary layer however model accuracy reduced close to the shoreline power spectra of observed and simulated velocity time series at different locations showed that the hydrodynamic model was able to describe the energy contained in the inertial scales but over predicted turbulent dissipation rates as a result model predicted values of energy in the smaller dissipation scales were lower compared to values calculated from observations in the cbl differences between energy contained in the observed and simulated velocity spectra increased as the shoreline is approached observations showed that vertical variations in the alongshore and cross shore velocities were dominated by inertial waves inaccuracies in representing energy dissipation rates and processes not explicitly described in the hydrodynamic model e g anisotropy waves could potentially contribute to errors in describing transport in the cbl measurements from a continuous dye release experiment from a riverine outfall were described using a nearshore model with a mean horizontal dispersion coefficient of 5 6 m2 s improved representations of physical processes such as turbulence internal waves and wave current interactions can be expected to provide better descriptions of solute transport in the cbl

relative effects of wind stress curl topography and stratification on large scale circulation in lake michigan 1 this paper uses the results from two multiseason numerical model simulations of lake michigan hydrodynamics to examine the relative effects of wind stress curl topography and stratification on large scale circulation the multiseason simulations provide a period long enough to encompass the full range of atmospheric and thermal conditions that can occur in the lake the purpose of this paper is to diagnose the relative importance of various mechanisms responsible for the large scale circulation patterns by analyzing the vorticity balance in the lake on a monthly timescale five different model scenarios are used to isolate the predominant mechanisms 1 baroclinic lake spatially variable wind stress 2 barotropic lake spatially variable wind stress 3 baroclinic lake spatially uniform wind stress 4 barotropic lake spatially uniform wind stress and 5 barotropic lake linearized equations spatially uniform wind stress by comparing the results of these five model scenarios it is shown that the cyclonic wind stress curl in the winter and the effect of baroclinicity in the summer are primarily responsible for the predominantly cyclonic flow in the lake topographic effects are also important but are not as significant as wind stress curl and baroclinic effects nonlinear effects are much smaller

onshore offshore correlations of cretaceous fluvial deltaic sequences southern baltimore canyon trough we evaluate cretaceous depositional sequences on approximately 4400 km 2700 mi of newly released multichannel seismic profiles and five wells on the continental shelf in the southern baltimore canyon trough and tie the data to three wells drilled onshore in the maryland coastal plain seismic geometries coupled with facies and biostratigraphy from the wells are used to delineate mid cretaceous aptian turonian depositional sequences and paleogeography beneath these sequences 400 1000 m 1300 3300 ft of lower cretaceous sedimentary rocks underlie the modern shelf they thicken along strike to the southwest implying a southern sediment source aptian to cenomanian sediments were deposited in shelf to nearshore settings a landward movement of the depocenter and a shift toward facies indicative of deeper paleodepths marks a 107 yr mid cretaceous transgression within which we identify five sequences a composite maximum flooding surface mfs within the uppermost of these retrogradational units is associated with the cenomanian turonian boundary and ocean anoxic event 2 shingled lower turonian seismic reflections prograde across the outer shelf downlapping onto the composite mfs and are truncated by a mid turonian sequence boundary the upper cretaceous section thickens seaward and along strike to the northeast implying a northern source and little late cretaceous accommodation beneath the modern shelf mid cretaceous strata offshore maryland are likely sand prone considering their proximity to the correlative fluvial facies of the onshore potomac group these potential reservoir sands are capped by regional confining units generated by 107 yr global mean sea level flooding events and are excellent targets for supercritical carbon storage

20 myr of eccentricity paced lacustrine cycles in the cenozoic ebro basin abstract long period orbital forcing is a crucial component of the major global climate shifts during the cenozoic as revealed in marine pelagic records a complementary regional perspective of climate change can be assessed from internally drained lake basins which are directly affected by insolation and precipitation balance the ebro basin in northeastern iberia embraces a 20 myr long continuous sedimentary record where recurrent expansions and retractions of the central lacustrine system suggest periodic shifts of water balance due to orbital oscillations in order to test climatic orbital forcing a key piece of the basin the los monegros lacustrine system has been analyzed in detail the cyclostratigraphic analysis points to orbital eccentricity as pacemaker of short to long term lacustrine sequences and reveals a correlation of maxima of the 100 kyr 400 kyr and 2 4 myr eccentricity cycles with periods of lake expansion a magnetostratigraphy based chronostratigraphy of the complete continental record allows further assessing long period orbital forcing at basin scale a view that challenges alternate scenarios where the stratigraphic architecture in foreland systems is preferably associated to tectonic processes we conclude that while the location of lacustrine depocenters reacted to the long term tectonic driven accommodation changes shorter wavelenght oscillations of lake environments still million year scale claims for a dominance of orbital forcing we suggest a decoupling between tectonic supply driven clastic sequences fed from basin margins and climatic base level driven lacustrine sequences in active settings with medium to large sediment transfer systems

geomagnetic field stability reversal events and excursions abstract it has been suggested that there are several reverse subchrons in the brunhes and this suggestion is gaining some acceptance however such a suggestion has fundanmental implications for the reversal process because it implies that the reverse polarity state has been substantially less stable than the normal polarity state during the brunhes chron analysis of the latest polarity reversal timescale confirms that there is no reason to reject the hypothesis of a common stability for the two polarity states the cretaceous superchron appears to be a time when the reversal rate slowed to the point where the reversal process actually halted so does not indicate any difference in the stability of the two polarity states after examining the data we found no convincing evidence for even a single reversal event during the brunhes and we conclude that the only reversal excursions that are sufficiently well documented for the brunhes are the laschamp and the blake further we note that the question of whether of large excursions represent aborted reversals is unresolved so excursion data should not at this stage be grouped with transition polarity data finally we note that most of the time the nearly axially symmetric normal and reverse polarity states appear to be remarkably stable

plate wide stress relaxation explains european palaeocene basin inversions during late cretaceous and cenozoic times many palaeozoic and mesozoic rifts and basin structures in the interior of the european continent underwent several phases of inversion the process of shortening a previously extensional basin 1 the main phases occurred during the late cretaceous and middle palaeocene and have been previously explained by pulses of compression mainly from the alpine orogen2 3 4 5 here we show that the main phases differed both in structural style and cause the cretaceous phase was characterized by narrow uplift zones reverse activation of faults crustal shortening and the formation of asymmetric marginal troughs in contrast the middle palaeocene phase was characterized by dome like uplift of a wider area with only mild fault movements and formation of more distal and shallow marginal troughs a simple flexural model explains how domal secondary inversion follows inevitably from primary convergence related inversion on relaxation of the in plane tectonic stress the onset of relaxation inversions was plate wide and simultaneous and may have been triggered by stress changes caused by elevation of the north atlantic lithosphere by the iceland plume6 or the drop in the north south convergence rate between africa and europe7

non hotspot volcano chains originating from small scale sublithospheric convection 1 some oceanic volcano chains violate the predictions of the hotspot hypothesis for geographic age progressions one mechanism invoked to explain these observations is small scale sublithospheric convection ssc in this study we explore this concept in thermo chemical 3d numerical models melting due to ssc is shown to emerge in elongated features 750 km parallel to plate motion and not just at a fixed spot therefore volcanism occurs in chains but not with hotspot like linear age progressions the seafloor age at which volcanism first occurs is sensitive to mantle temperature as higher temperatures increase the onset age of ssc because of the stabilizing influence of thicker residue from previous mid ocean ridge melting mantle viscosity controls the rate of melt production with decreasing viscosities leading to more vigorous convection and volcanism calculations predict many of the key observations of the pukapuka ridges and the volcano groups associated with the line cook austral and marshall islands