investigation of the causes of historical changes in the subsurface salinity minimum of the south atlantic in this study we investigate the subsurface salinity changes on decadal timescales across the subtropical south atlantic ocean using two ocean reanalysis products the latest version of the simple ocean data assimilation and the estimating the circulation and climate of the ocean phase ii as well as using additional climate model experiments results show that there is a recent significant salinity increase at the core of the salinity minimum at intermediate levels the main underlying mechanism for this subsurface salinity increase is the lateral advective gyre changes due to the southern annular mode variability which conditions an increased contribution from the indian ocean high salinity waters into the atlantic the global warming signal has a secondary but complementary contribution latitudinal differences at intermediate depth in response to large scale forcing are in part caused by local variation of westward propagation features and by compensating contributions of salinity and temperature to density changes

late eocene and maastrichtian paleomagnetic poles for the pacific plate implications for the validity of seamount paleomagnetic data abstract mean paleomagnetic poles for the pacific plate have been calculated for the late eocene 39 ma and the maastrichtian 69 ma the former is located at 77 6 n 7 6 e the latter at 69 9 n 0 9 e although these pole positions are little changed from previous calculations they are better constrained with additional data slightly less than half of the data are derived from the inversion of seamount magnetic fields providing an excellent opportunity to compare such data with other paleomagnetic data of the same age as no significant systematic difference between the two types of data is evident it is inferred that most seamount paleomagnetic data are probably useful indicators of the paleomagnetic field direction

on the use of seismic data to monitor the injection of co2 into a layered aquifer abstract one method to monitor the migration of co2 through a confined layered aquifer is to use time lapse seismic reflection data we examine how such information may be combined with a flow model for a co2 plume spreading through a water saturated aquifer to provide constraints on the migration of a plume of injected co2 we focus on the estimation of the partitioning of the injected flux between the different layers in a multi layer geological formation and on estimation of the permeability of each layer since there is a minimum depth of the injected co2 which is detectable seismically we show that even in a one layer formation the model predicts two different possible permeabilities for the formation corresponding to a fast pressure driven flow and a slower buoyancy controlled flow these two estimates of the permeability are sensitive to changes in the seismic detection threshold if there is additional data on the bottom hole well pressure we can distinguish between the solutions in a multi layer system supplied from a single well the non uniqueness in the inversion process leads to uncertainty in both the partitioning of the flux between the layers and the permeability of the different layers in the formation the model constraints lead to a relatively small range of possible distributions of the flux but if there is a lack of information about the relative pressure in the different layers near the well there is a much larger range of possible values for the permeability of each layer we develop some simple bounds on the problem by considering the case in which the near well pressure difference between the layers is related to either the vertical hydrostatic or the vertical co2 static pressure difference we examine the implications of the technique for interpreting the historic data set relating to co2 injection at the sleipner field north sea in which there are nine distinct layers in the formation this leads to estimates for the possible flux partitioning between the layers and also some constraints on the possible range of effective permeability in each layer estimates of the partitioning of the flux can inform estimates of the efficiency of co2 injection in the different layers however the uncertainty in the estimate of the effective permeability leads to uncertainty in estimates of the propagation speed of the flow in each layer and hence assessments of the hazards of leakage and of the rate of capillary trapping or dissolution of co2 following injection

analytical solutions for leakage rates through abandoned wells 1 disposal of waste fluids via injection into deep saline aquifers is practiced in a variety of industries injection takes place in sedimentary basins that often have a history of oil and gas exploration and production which means that wells other than those used for waste disposal may exist in the vicinity of the injection site these existing wells provide possible pathways for leakage of waste fluids toward the shallow subsurface and the land surface for single phase flows of liquids with essentially constant properties the equations governing the system are linear and solutions may be written using the superposition principle because leakage through existing wells produces a time varying flux rate the solution of the governing equations involves convolution integrals previous solutions have addressed the problem of one injection well one existing passive well and a simple geometry of two aquifers separated by an aquitard by use of laplace transforms even for this simple case inversion of the transform is difficult solutions involving more than one passive well have not been developed nor have solutions been developed for more than two aquifers and one aquitard realistic injection cases often involve layered systems with multiple aquifers and aquitards as well as multiple passive wells sometimes numbering in the hundreds solutions for the general case of multiple aquifers and wells may be developed through introduction of approximations to the well function and appropriate simplification of the convolution integral such a solution is computationally simple comparison to solutions using the full laplace transform solution indicates that the new solution procedure produces excellent results application of the new solution to a case of multiple passive wells shows that the cumulative leakage flux in the passive wells is not a simple sum of the single well case owing to leakage induced drawdown around the passive wells in addition application to the case of multiple aquifers and aquitards demonstrates the importance of leakage into intervening aquifers as a mechanism to mitigate leakage into shallow zones a process referred to as the elevator model the new analytical solution provides a tool to analyze practical injection problems and forms a foundation on which more complex solutions such as those involving injection of a nonaqueous fluid into a deep brine formation may be based

draining viscous gravity currents in a vertical fracture we consider the flow of instantaneous releases of a finite volume of viscous fluid in a narrow vertical fracture or hele shaw cell when there is a still narrower vertical crack in the horizontal base of the cell the predominant motion is over the horizontal surface but fluid also drains through the crack progressively diminishing the volume of the current in the fracture when the crack is shallow on the scale of the current it saturates immediately with the draining fluid in this case we obtain an exact analytical solution for the motion when the crack is deeper and does not saturate immediately we calculate numerically the motion of the fluid in both the fracture and the crack in each case the current advances to a finite run out length and then retreats we describe both phases of the motion and characterize the run out length in terms of the controlling parameters

modeling leakage pathways in subsurface formations fluid drainage through multiple fractures in porous media insights from hele shaw cell experiments abstract arresting the recent observed warming of the earth s climate is a challenge requiring the reduction of anthropogenic emissions of carbon dioxide one option for reducing emissions into the atmosphere is to capture and sequester the released carbon dioxide in geological formations however potential geological storage first requires a risk assessment of carbon dioxide escaping to overlying layers and back to the atmosphere through leakage pathways in the formation this in turn requires an understanding of fluid flow through the leakage pathways in this study the effect of leakage pathways on the flow of a gravity current was investigated using an analogue system a hele shaw cell fluid was introduced through the top edge of the cell and flowed out through one or more holes in its impermeable base the height of the accumulated fluid above the base of the cell at various points along its length and the outflow rate of fluid through the holes was measured this measurement was conducted with varying conditions of the location number and strength of source as well as the location and number of holes at steady state the fluid motion was in accordance with darcy s law for horizontal flow in a long thin current in another set of experiments in which inflow was stopped and the fluid was allowed to drain out of a single open hole the outflow rate was in accordance with darcy s law for one dimensional flow in the vertical direction until the fluid height above the hole fell below a certain limit this threshold height was found to be 1 3 cm which was similar in magnitude to the length of the hole a time series of photographs tracked the flow of colored dye the photographs demonstrated that at steady state the fluid traveled for some distance beyond the hole before draining through it this implies that contaminants may be transported in a formation even beyond an outlet before finally draining out through it the photographs also documented the shape of the interface between the newly introduced dye and the ambient fluid in the cell these shapes were found to be different in a cell placed horizontally versus one placed on an incline suggesting that the geometry and flow conditions in a formation affecting the transport of an injected fluid these findings may be used as a basis for predicting behavior of a fluid injected into a fractured formation in the subsurface

subduction and transport in the indian and pacific oceans in a 2 co2 climate abstract subduction water mass transformation and transport rates in the indo pacific ocean are diagnosed in a recent version of the canadian centre for climate modelling and analysis coupled model it is found that the subduction across the base of the winter mixed layer is dominated by the lateral transfer particularly within the relatively dense water classes corresponding to the densest mode and intermediate waters however within lighter densities including those characterizing the lighter varieties of mode waters the vertical transfer has a strong positive input to the net subduction the upper ocean volume transports across 30 n and 32 s are largest within the density classes that correspond to mode waters in the north pacific the buoyancy flux converts the near surface waters mostly to denser water classes whereas in the southern ocean the surface waters are transformed both to lighter and denser water classes depending on the density in response to a doubling of co2 the subduction tr

modelling carbon dioxide accumulation at sleipner implications for underground carbon storage an analytical solution to the equations describing the flow of a buoyant fluid released into a porous medium below a horizontal impermeable boundary is used to model the growth of co2 accumulations beneath thin mudstone beds in the utsira sand reservoir at sleipner in the north sea here supercritical co2 has been injected at a rate of 1 mt yr since 1996 and imaged by time lapse seismic data in 1999 2001 and 2002 the co2 rises as a narrow plume and is partially trapped by a number of thin mudstones before reaching the caprock to the reservoir the radii of the individual layers of trapped co2 increase as the square root of time since initiation as predicted by the modelling for constant input flux however apparent negative initiation times for horizons low in the reservoir suggests that net input fluxes for these layers have decreased with time most probably as the spreading layers have increased their leakage rates accumulation of co2 in the layers higher in the reservoir was initiated up to 3 yr after injection started modelling of the thickness profiles across three of the higher layers suggests that their net input fluxes have increased with time the observation that the central thicknesses of the deeper layers have remained approximately constant or have slightly decreased since first imaged in 1999 is consistent with the model predictions that the central thickness is directly proportional to net input flux however estimates of the permeability of the reservoir from the rate of increase of the radii of the co2 accumulations are an order of magnitude less than measured permeabilities on the reservoir sandstone permeabilities estimated from the modelling of layer thickness changes scatter in the same range these discrepancies may arise from 1 approximations in the model not being valid 2 the measured permeabilities not being representative of the permeability for two phase flow on the scale of the reservoir or considered less likely 3 that much less co2 is being stored in the imaged co2 accumulations than estimated from the seismic reflection profiles the most probable cause of the discrepancy is that the relative permeability for the co2 phase is significantly reduced at lower co2 saturations

palaeomagnetism of cretaceous pacific seamounts summary the palaeomagnetism of cretaceous pacific seamounts as deduced from their magnetic anomalies is reviewed results from 35 seamounts are reported here for the first time of these 35 results 15 are of high enough quality to be useful this has resulted in a considerable increase in the available information concerning the palaeomagnetism of the pacific plate using only the most reliable results we calculate a palaeomagnetic pole for the upper cretaceous at 58 north 350 east with a 95 per cent cone of confidence of only 5 this pole is considerably more accurate than the one previously reported and is farther to the west the previously reported difference between the mean pole position from seamounts close to japan and the mean pole position from seamounts close to hawaii is not real although one group of seamounts close to japan gives an anomalous pole position several mechanisms have been suggested whereby errors might be introduced in the determinations of pole positions from seamounts no error is introduced in the pole position because of the restricted extent of surveys and the consequent inaccuracy in the determination of the regional field the demagnetization effect which can produce differences between the observed direction of magnetization and the direction of the magnetizing field in an elongated body is unimportant for seamounts the new pole position is sufficiently accurate for use in many types of calculations in which it is desired to locate the pacific plate with respect to the earth s spin axis

the effect of a fissure on storage in a porous medium we consider the two dimensional buoyancy driven flow of a fluid injected into a saturated semi infinite porous medium bounded by a horizontal barrier in which a single line sink representing a fissure some distance from the point of injection allows leakage of buoyant fluid our studies are motivated by the geological sequestration of carbon dioxide co2 and the possibility that fissures in the cap rock may compromise the safe long term storage of co2 a theoretical model is presented that accounts for leakage through the fissure using two parameters which characterize leakage driven both by the hydrostatic pressure within the overriding fluid and by the buoyancy of the fluid within the fissure we determine numerical solutions for the evolution of both the gravity current within the porous medium and the volume of fluid that has escaped through the fissure as a function of time a quantity of considerable practical interest is the efficiency of storage which we define as the amount of fluid remaining in the porous medium relative to the amount injected this efficiency scales like t 1 2 at late times indicating that the efficiency of storage ultimately tends to zero we confirm the results of our model by comparison with an analogue laboratory experiment and discuss the implications of our two dimensional model of leakage from a fissure for the geological sequestration of co2

converging gravity currents over a permeable substrate we study the propagation of viscous gravity currents along a thin permeable substrate where slow vertical drainage is allowed from the boundary in particular we report the effect of this vertical fluid drainage on the second kind self similar solutions for the shape of the fluid fluid interface in three contexts i viscous axisymmetric gravity currents converging towards the centre of a cylindrical container ii viscous gravity currents moving towards the origin in a horizontal hele shaw channel with a power law varying gap thickness in the horizontal direction and iii viscous gravity currents propagating towards the origin of a porous medium with horizontal permeability and porosity gradients in power law forms for each of these cases with vertical leakage we identify a regime diagram that characterizes whether the front reaches the origin or not in particular when the front does not reach the origin we calculate the final location of the front we have also conducted laboratory experiments with a cylindrical lock gate to generate a converging viscous gravity current where vertical fluid drainage is allowed from various perforated horizontal substrates the time dependent position of the propagating front is captured from the experiments and the front position is found to agree well with the theoretical and numerical predictions when surface tension effects can be neglected

modelling carbon dioxide sequestration in layered strata motivated by the geological sequestration of carbon dioxide co2 we study the propagation of gravity currents in a porous medium bounded by a thin layer of much lower permeability we formulate a model for drainage assuming that the fluid remains simply connected throughout using this model we examine the propagation of both two dimensional and axisymmetric currents numerically we find that for the fixed flux situation solutions approach a steady state which is described analytically the approach to this final solution depends on both the permeability contrast and thickness of the thin layer and in many cases the current first overshoots before relaxing back to its ultimate steady state finally we examine propagation along multiple thin lower permeability layers as a reduced order model of the plume of co2 currently being injected at sleipner in the north sea

cenozoic plate kinematics subduction and magmatism south american andes revised plate reconstructions and enlarged isotopic age data sets strongly support three mechanisms for controlling the configuration and associated volcanism and tectonism of the andean subduction zone these include age of subducted plate convergence rate and interaction with hotspot traces from 50 to 25 ma in the andes the age of oceanic plate subducted progressively decreased apparently resulting in a9gradual decrease in subduction angle and consequent eastward shift in the loci of magmatic activity a major reorganization of plate motions at 25 ma resulted in an increased convergence rate normal to the chilean andes and was accompanied by subsequent broadening of the locus of magmatic activity into adjacent portions of bolivia and argentina convergence rates changed only slightly across the peruvian margin and no clear effect on subsequent magmatism is indicated interaction of the andean subduction zone with the juan fernandez and easter nazca hotspot traces apparently resulted in lower angle subduction and consequent gaps in magmatic activity as predicted continuations of the traces correspond with regions lacking dated volcanic rocks the current gaps in igneous activity correspond with contemporary subduction of the two traces and this association apparently occurred in the past as well

paleomagnetism of cretaceous pacific seamounts revisited the paleomagnetism of cretaceous pacific seamounts is reexamined herein techniques for nonuniform magnetic modeling are applied to determine paleomagnetic pole positions and their associated confidence limits modeling techniques are presented for reconstruction of both uniform and nonuniform components of the seamount magnetization the uniform component yields an estimate of the paleomagnetic pole position and the nonuniform component accounts for irregularities in the seamount magnetization a seminorm minimization approach constructs maximally uniform magnetizations and is used to represent seamount interiors a statistical modeling approach constructs random nonuniform magnetizations and is used to determine the confidence limits associated with each pole position mean paleopoles are calculated for groups of seamounts including their associated error bounds the mean paleopole for seven reliably dated upper cretaceous seamounts is located close to the position predicted by pacific hotspot relative motion the paleopole for five seamounts with cretaceous minimum dates is located west of the hotspotpredicted apparent polar wander path and may represent a lower cretaceous or upper jurassic pole

spatial and temporal variations in the andean subduction zone a comprehensive global study of the process of subduction of oceanic lithosphere has made it evident that a major role is played by the age of the subducted lithosphere the age dependence of subduction is of special interest in an understanding of the late cenozoic history of the andean subduction zone many of the complexities of this zone result from the peculiar circumstance that the zone is in transition from an early stage of consumption of old lithosphere 70 ma producing deep earthquakes towards the latest stage of consumption of young lithosphere without deep earthquakes this transition has induced an evolutionary pattern with significant temporal variations notably changes in dip and length of the subducted slab moreover the various segments of the south american subduction zone are in different stages of this evolution in comparison with the other segments the northern chile segment is in the earliest stage and therefore shows a much closer resemblance to the classic deep subduction zones in the western pacific than do other parts of the south american zone a roughly n s symmetry in development is found around northern chile with the ecuadorian and southern chilean near 40 45 s segments representing the latest stage to a large extent the temporal and spatial variations in lithospheric age at the trench originate from the reorganization in plate configuration which started with the break up of the farallon plate into the cocos plate and the nazca plate at about 25 ma

plate reconstructions aseismic ridges and low angle subduction beneath the andes low angle subduction segments beneath peru and chile are believed to represent interaction of the subduction zone with the aseismic nazca and juan fernandez ridges on the basis of symmetric sea floor spreading models and plate hotspot reconstructions predicted continuations of the relatively buoyant ridges correspond well with the limits of the low angle subduction segments further the history of interaction of the aseismic ridges with the subduction zone as predicted by plate reconstructions is not inconsistent with available information on volcanic episodes of the andes if the contemporary correlation of volcanic gaps and low angle subduction is also applicable to the rest of the late cenozoic the occurrence of deep seismicity beneath the eastern flanks of the andes is also believed to reflect the effects of low angle subduction the deep seismic segments are adjacent to segments which are presently or were recently experiencing low angle subduction thus the deep seismicity is interpreted as representative of remnants of normal oceanic lithosphere subducted before interaction of aseismic ridges with the subduction zone other geologic phenomena are associated with low angle subduction beneath south america including landward shift in loci of tectonism surficial subsidence and laramide style deformation the aseismic ridge buoyancy hypothesis appears to be a valuable predictive tool for the interpretation of such geologic effects

changes in subduction in the south atlantic ocean during the 21st century in the ccsm3 1 the community climate system model version 3 is used to analyse changes in water mass subduction rates in the south atlantic ocean over the 21st century the model results are first compared to observations over 1950 2000 and shown to be rather good the subduction rates do not change significantly over the 21st century but the densities at which water masses form become significantly lighter the strong westerly winds in this region do not change much which suggests small changes to the rate at which the atlantic sector of the southern ocean takes up heat and carbon dioxide over the 21st century

late cretaceous apparent polar wander of the pacific plate evidence for a rapid shift of the pacific hotspots with respect to the spin axis paleomagnetic data from the pacific plate show that the average azimuth of the pacific plate decreased by 12 between 90 ma and 81 ma whereas trends of late cretaceous seamount chains suggest that the pacific plate moved northwestward relative to the hotspots with little change in azimuth during the same time interval this difference is used to infer a 13 4 shift of the spin axis relative to the hotspots in the pacific ocean basin this shift occurred within 5 m y of the occurrence of anomalous behavior of the paleomagnetic field recorded in anomalies 33 and 34 this coincidence in timing suggests there may be a causal link between these three phenomena

solar modulation of north atlantic central water formation at multidecadal timescales during the late holocene article i nfo understanding natural climate variability in the north atlantic region is essential not only to assess the sensitivity of atmosphere ocean climate signal exchange and propagation but also to help distinguish between natural and anthropogenic climate change the north atlantic oscillation is one of the controlling modes in recent variability of atmosphere ocean linkages and ice freshwater fluxes between the polar and north atlantic ocean through these processes the nao influences water mass formation and the strength of the atlantic meridional overturning circulation and thereby variability in ocean heat transport however the impact of the nao as well as other forcing mechanisms on multidecadal timescales such as total solar irradiance on eastern north atlantic central water production central water circulation and climate signal propagation from high to low latitudes in the eastern subpolar and subtropical basins remains uncertain here we use a 1200 yr long benthic foraminiferal mg ca based temperature and oxygen isotope record from a 900 m deep sediment core off northwest africa to show that atmosphere ocean interactions in the eastern subpolar gyre are transferred at central water depth into the eastern boundary of the subtropical gyre further we link the variability of the nao over the past 165 yrs and solar irradiance late holocene and their control on subpolar mode water formation to the multidecadal variability observed at mid depth in the eastern subtropical gyre our results show that eastern north atlantic central waters cooled by up to 0 8 0 7 c and densities decreased by 0 3 0 2 during positive nao years and during minima in solar irradiance during the late holocene the presented records demonstrate the sensitivity of central water formation to enhanced atmospheric forcing and ice freshwater fluxes into the eastern subpolar gyre and the importance of central water circulation for cross gyre climate signal propagation during the late holocene 2011 elsevier b v all rights reserved

effects of in situ conditions on relative permeability characteristics of co2 brine systems carbon dioxide capture and geological storage ccgs is an emerging technology that is increasingly being considered for reducing greenhouse gas emissions to the atmosphere deep saline aquifers provide a very large capacity for co2 storage and unlike hydrocarbon reservoirs and coal beds are immediately accessible and are found in all sedimentary basins proper understanding of the displacement character of co2 brine systems at in situ conditions is essential in ascertaining co2 injectivity migration and trapping in the pore space as a residual gas or supercritical fluid and in assessing the suitability and safety of prospective co2 storage sites because of lack of published data the authors conducted a program of measuring the relative permeability and other displacement characteristics of co2 brine systems for sandstone carbonate and shale formations in central alberta in western canada the tested formations are representative of the in situ characteristics of deep saline aquifers in compacted on shore north american sedimentary basins the results show that the capillary pressure interfacial tension relative permeability and other displacements characteristics of co2 brine systems depend on the in situ conditions of pressure temperature and water salinity and on the pore size distribution of the sedimentary rock this paper presents a synthesis and interpretation of the results

on the slow draining of a gravity current moving through a layered permeable medium we examine the gravitational dispersal of dense fluid through a horizontal permeable layer which is separated from a second underlying layer by a narrow band of much lower permeability we derive a series of analytical solutions which describe the propagation of the fluid through the upper layer and the draining of the fluid into the underlying region the model predicts that the current initially spreads according to a self similar solution however as the drainage becomes established the spreading slows and in fact the fluid only spreads a finite distance before it has fully drained into the underlying layer we examine the sensitivity of the results to the initial conditions through numerical solution of the governing equations we find that for sources of sufficiently large initial aspect ratio defined as the ratio of height to length the solution converges rapidly to the initially self similar regime for longer and shallower initial source conditions this convergence does not occur but we derive estimates for the run out length of the current which compare favourably with our numerical data we also present some preliminary laboratory experiments which support the model

early time periodic injection and extraction in an inclined confined aquifer we consider the periodic injection and extraction of fluid from a horizontal line well in an inclined saturated aquifer of finite thickness h as part of an aquifer thermal energy storage system we focus on the case in which the injected fluid is dense relative to the original fluid in the aquifer and hence tends to run off downslope so that during the extraction cycle a mixture of original aquifer fluid and injected fluid is produced we study the controls on the composition of the extracted fluid distinguishing between the cases where there is an open boundary downslope or upslope of the source with the other boundary being sealed we find that initially the fraction of original aquifer fluid recovered during an extracted cycle decreases from cycle to cycle and at long times this fraction asymptotes to a value mathscr f 0 that depends on it gamma h s cos it theta it phi 2 it tau q 2 1 3 and it pi hs sin it theta it phi q where it tau is the time period of injection it phi is the porosity of the aquifer q is the injection rate s is the speed of the buoyancy driven flow and it theta is the angle of inclination to the horizontal at long times the flow asymptotes to a quasi steady exchange flow solution that develops in an inclined saturated porous layer of thickness h in contact with a stratified fluid reservoir filled to thickness h 0 it gamma it pi h with relatively dense fluid this enables us to calculate the average composition of the extracted fluid which is of concern if the original aquifer fluid contains contaminants since the produced aquifer fluid is driven by this quasi steady exchange flow we show that contaminants downslope of the well will be produced after a finite time whereas contaminants upslope of the well typically remain in the aquifer irrespective of the far field boundary conditions we successfully test the models with a series of analogue experiments of both the injection extraction flow and the exchange flow using a hele shaw cell

the paleomagnetism of eastern nazca plate seamounts abstract paleomagnetism of eastern nazca plate seamounts defines nazca and farallon absolute plate motion during cenozoic times magnetic and bathymetric surveys are presented for two eastern nazca plate seamounts in the chile basin and they are used to calculate paleomagnetic poles with uniform and nonuniform magnetic modeling the paleopole for piquero 2 seamount is coincident with the earth s pole suggesting a young seamount the paleopole for piquero 1 seamount indicates that the nazca plate moved 23 northward during 0 50 ma this is 13 more latitudinal motion than predicted by a pacific hotspot reference frame and 20 more motion than predicted by dsdp sediment and basalt paleomagnetism

paleomagnetism of abbott seamount and implications for the latitudinal drift of the hawaiian hot spot the magnetic anomaly of abbott seamount located near the hawaiian emperor bend has been analyzed for its paleomagnetic information short wavelength noise components of the anomaly assumed to result from small magnetization inhomogeneities or reversals in the upper layers of the volcano were filtered out by upward continuation the polarity of the bulk of the seamount is reversed and its virtual geomagnetic pole is located at 75 5 n 4 6 e this pole lies close to pacific paleomagnetic poles of late eocene age and is consistent with the age of the edifice to be expected from its position in the hawaiian chain the paleolatitude of the seamount 17 5 n 4 4 is not significantly different from the present latitude of the hawaiian hot spot approximately 19 5 n this finding implies that the hawaiian hot spot and by inference other hot spots has remained relatively fixed with respect to the spin axis since the eocene however other paleolatitudes from the hawaiian emperor chain suggest that systematic variation of the hot spot s latitude may have occurred comparison of the hawaiian emperor paleolatitude data with paleomagnetic data from central pacific piston cores and with north pacific paleoequator data from deep sea drilling project cores indicates that the apparent latitude drift since the eocene has been largely the result of long term nondipole components in the geomagnetic field rather than relative motion between the hot spot and the spin axis conversely the variation that occurred prior to the eocene appears to contain a significant amount of such motion coupled with an indeterminate amount of nondipole effect

petrology and geochronology of volcanic rocks from seamounts along and near the hawaiian ridge implications for propagation rate of the ridge lavas from three seamounts along and three seamounts near the hawaiian ridge are petrographically and geochernically similar to lavas from the hawaiian islands rock types recovered include tholeftic and alkalic lavas the composition of these lavas is virtually identical to that of lavas from the hawaiian islands this indicates that the source composition and petrogenesis of lavas along the hawaiian chain are very consistent the three along ridge seamounts are in areas where there were gaps in the radiometric age data base new ages further document the linear age progression along the chain and define a new propagation rate of 9 6 0 4 cm yr which is identical to the present day plate motion of the island of hawaii the near ridge seamounts are cretaceous in age 74 77 ma and are part of nnw trending linear chains that predate and are unrelated to the nw and n trending hawaiian and emperor chains

impacts of climate change on the subduction of mode and intermediate water masses in the southern ocean abstract changes in the temperature salinity and subduction of subantarctic mode water samw and antarctic intermediate water aaiw between the 1950s and 2090s are diagnosed using the csiro mark version 3 5 mk3 5 climate system model caps under a co2 forcing that reaches 860 ppm by the year 2100 these southern ocean upper limb water masses ventilate the ocean interior and changes in their properties have been related to climate change in numerous studies over time the authors follow the low potential vorticity and salinity minimum layers describing samw and aaiw and find that the water column in the 2090s shifts to lighter densities by approximately 0 2 kg m 3 the model projects a reduction in the samw and aaiw annual mean subduction rates as a result of a combination of a shallower mixed layer increased potential vorticity at the base of the mixed layer and a net buoyancy gain there is little change in the projected total volume of samw transported into the ocean interior via the subduction

capillary entry pressure and the leakage of gravity currents through a sloping layered permeable rock we examine the motion of a buoyant fluid injected into a water saturated porous rock as it spreads along a thin inclined low permeability barrier we account for leakage of the fluid across the barrier once the current is sufficiently deep so that the pressure exceeds the capillary threshold we show that at some distance from the source the pressure decreases below this threshold and all the remaining flux spreads laterally along the barrier we examine the controls on the partitioning of the flow between the draining flux and the laterally spreading flux and also the controls on the lateral extent of the draining region for the case of an instantaneous release and a maintained release of fluid we consider the implications of our work for the dispersal of co 2 plumes which may be sequestered in deep saline aquifers

the effect of drainage on the capillary retention of co2 in a layered permeable rock buoyant plumes of co 2 spreading through water saturated permeable rock bounded by layers of lower permeability tend to spread laterally as they advance they may gradually leak through fractures or discontinuities in the lower permeability boundary leading to a gradual waning of the original plume and dispersal of co 2 higher in the formation with a finite release of co 2 the trailing edge of the plume recedes with time and capillary forces tend to trap a fraction of this co 2 within the pore space this also leads to a gradual waning of the plume with time and limits the mass of co 2 which can leak through the boundary and rise higher into the formation we explore the balance between these two effects and calculate some of the controls on the fraction of the co 2 plume which becomes trapped within the original layer of rock

on the flow of buoyant fluid injected into a confined inclined aquifer we study the dispersal of a plume of incompressible buoyant fluid injected into a confined sloping aquifer which has an outflow at a single fault which may be up dip up slope or down dip down slope from the point of injection we develop a long time asymptotic solution for the motion of the injected fluid we show that for the case in which the outflow fault is up dip from the point of injection there is a critical injection rate above which the injected fluid floods the full depth of the aquifer and we show that for the case in which the outflow fault is down dip from the point of injection there is a critical injection rate below which all injected fluid initially flows up dip our analysis leads to expressions for the lateral extent of the injected fluid as a function of time and we consider the implications of the model for the dispersal of supercritical carbon dioxide injected into deep saline aquifers the work also indicates that the geometry of the system may have a significant effect on i the total volume of carbon dioxide which it is possible to sequester in a faulted aquifer and ii the interpretation of the dispersed position of any injected tracers

cenozoic global plate motions cenozoic global plate motions relative to the hot spots are investigated and compared to plate motions in a mean lithosphere reference frame plate motions were analyzed over six time intervals divided by ages 10 25 43 48 and 56 ma chosen as much as possible to coincide with key plate reorganizations alternative motion circuits and rotational parameters were considered and evaluated with paleomagnetic data from the pacific and north american plates the circuit found to be in best agreement with the paleomagnetic data is one in which the hot spots in the atlantic region are assumed to be fixed relative to the hot spots in the pacific region throughout the cenozoic the hot spot and mean lithosphere reference frames have been in continual slow relative motion the rate of motion is nonuniform however most of the motion having occurred during the middle cenozoic the net cenozoic rotation of the lithosphere relative to the hot spots is described by a right handed rotation of 7 about a euler pole at 46 s 87 e which yields a 5 displacement of the north poles of the two reference frames this motion is small enough that inferences drawn about plate speeds in one reference frame should be valid in the other analysis of the global motions resulting from our preferred model showed that many characteristics of current plate motions have persisted throughout the cenozoic plate speeds correlate with latitude plates moving faster near the equator than near the poles throughout the cenozoic as at present continental plates except for the indian plate moved slower than oceanic plates throughout the cenozoic even the structure of the velocity fields as revealed in a contour of root mean square velocities in equatorial bands persists throughout the cenozoic the migration of the paleomagnetic axis over time is also compared to the hot spot and mean lithosphere reference frames the paleomagnetic axis has shifted 5 10 relative to the hot spot frame and a lesser amount relative to the mean lithosphere frame

leakage from gravity currents in a porous medium part 2 a line sink we consider the propagation of a buoyancy driven gravity current in a porous medium bounded by a horizontal impermeable boundary the current is fed by a constant flux injected at a point and leaks through a line sink at a distance from the injection point this is an idealized model of how a fault in a cap rock might compromise the geological sequestration of carbon dioxide the temporal evolution of the efficiency of storage defined as the instantaneous ratio of the rate at which fluid is stored without leaking to the rate at which it is injected is of particular interest we show that the efficiency of storage decays like t 2 5 for times t that are long compared with the time taken for the current to reach the fault this algebraic decay is in contrast to the case of leakage through a circular sink neufeld et al j fluid mech vol 2010 where the efficiency of storage decays more slowly like 1 ln t the implications of the predicted decay in the efficiency of storage are discussed in the context of geological sequestration of carbon dioxide using parameter values typical of the demonstration project at sleipner norway we show that the efficiency of storage should remain greater than 90 on a time scale of millennia provided that there are no significant faults in the cap rock within about 12 km of the injection site

topographic controls on gravity currents in porous media we present a theoretical and experimental study of the propagation of gravity currents in porous media with variations in the topography over which they flow motivated in part by the sequestration of carbon dioxide in saline aquifers we consider cases where the height of the topography slopes upwards in the direction of the flow and is proportional to the nth power of the horizontal distance from a line or point source of a constant volumetric flux in two dimensional cases with n 1 2 the current evolves from a self similar form at early times when the effects of variations in topography are negligible towards a late time regime that has an approximately horizontal upper surface and whose evolution is dictated entirely by the geometry of the topography for n 0 result in a transition from an early time similarity solution towards a topographically controlled regime that has an approximately horizontal free surface we also analyse the evolution over topography that can vary with different curvatures and topographic exponents between the two horizontal dimensions finding that the flow transitions towards a horizontally topped regime at a rate which depends strongly on the ratio of the curvatures along the principle axes finally we apply our mathematical solutions to the geophysical setting at the sleipner field concluding that topographic influence is unlikely to explain the observed non axisymmetric flow

coherent response of antarctic intermediate water and atlantic meridional overturning circulation during the last deglaciation reconciling contrasting neodymium isotope reconstructions from the tropical atlantic antarctic intermediate water aaiw plays important roles in the global climate system and the global ocean nutrient and carbon cycles however it is unclear how aaiw responds to global climate changes in particular neodymium isotopic composition end reconstructions from different locations from the tropical atlantic have led to a debate on the relationship between northward penetration of aaiw into the tropical atlantic and the atlantic meridional overturning circulation amoc variability during the last deglaciation we resolve this controversy by studying the transient oceanic evolution during the last deglaciation using a neodymium enabled ocean model our results suggest a coherent response of aaiw and amoc when amoc weakens the northward penetration and transport of aaiw decreases while its depth and thickness increase our study highlights that as part of the return flow of the north atlantic deep water nadw the northward penetration of aaiw in the atlantic is determined predominately by amoc intensity moreover the inconsistency among different tropical atlantic end reconstructions is reconciled by considering their corresponding core locations and depths which were influenced by different water masses in the past the very radiogenic water from the bottom of the gulf of mexico and the caribbean sea which was previously overlooked in the interpretations of deglacial end variability can be transported to shallow layers during active amoc and modulates end in the tropical atlantic changes in the aaiw core depth must also be considered thus interpretation of end reconstructions from the tropical atlantic is more complicated than suggested in previous studies

andean tectonics related to geometry of subducted nazca plate seismological and geological data show that tectonic segmentation of the andes coincides with segmentation of the subducted nazca plate which has nearly horizontal segments and 30 east dipping segments andean tectonics above a flat subducting segment between 28 s to 33 s are characterized by from west to east 1 a steady topographic rise from the coast to the crest of the andes 2 no significant quaternary and possibly neogene magmatism 3 a narrow belt of eastward migrating apparently thin skinned neogene to quaternary shortening of the andes and 4 plio pleistocene uplift of the crystalline basement on reverse faults in the pampeanas ranges from about 15 to 24 s over a 30 dipping subducted plate a west to east andes cross section includes 1 a longitudinal valley east of coastal mountains 2 an active neogene and holocene andesitic volcanic axis 3 the altiplano puna high plateau 4 a high neogene but inactive thrust belt eastern cordillera and 5 an active eastward migrating subandean thin skinned thrust belt tectonics above a steeply subducting segment south of 33 s are similar west of the volcanic axis but quite different to the east early cenozoic tectonics of western north america were quite similar to the neogene andes however duration of segmentation was longer and the width of deformation was greater in the western united states patterns of crustal seismicity are systematically related to plio quaternary structural provinces implying that current deformational processes have persisted since at least the pliocene horizontal compression parallel to the plate convergence direction is indicated to a distance of 800 km from the trench above flat subducting segments crustal seismicity occurs over a broad region whereas over steep segments it is confined to the narrow thrust belt strain patterns in the forearc region are complex and perhaps extensional and a broad region of the altiplano puna and eastern cordillera appears to be aseismic

fluid transport in geological reservoirs with background flow this paper presents fundamental analysis of the injection and release of fluid into porous media or geological reservoirs saturated by a different fluid undergoing a background flow and tests the predictions using analogue laboratory experiments the study reveals new results important for an understanding of the transport of hazardous contaminants through aquifers and the long term fate of carbon dioxide in geological sequestration using numerical and asymptotic analysis we describe a variety of flow regimes that arise and demonstrate an almost instantaneous control of injected fluid by the far field conditions in geological reservoirs for a continuous input the flow develops a horizontal interface between the injected and ambient fluids the background flow thereby effectively caps the height of the injected fluid into a shallower region of vertical confinement for a released parcel of fluid gravitational spreading is found to become negligible after a short time a dominant control of the interface by the background pressure gradient arises and stems from the different velocities at which it drives the injected and ambient fluids individually similarity solutions describing these dynamics show that the parcel approaches a slender triangular profile that grows horizontally as where is time a rate faster than relaxation under gravity shock layers develop at the front or back of the parcel depending on whether it is more or less viscous than the ambient fluid new analytical results describing the long term effects of residual trapping due to capillary retention are developed which yield explicit predictions for the time and length scales on which a parcel of becomes retained we end by applying our results to geological contexts concluding that even slight background motion can have considerable implications for long term transport through the subsurface

a statistical theory of seamount magnetism the standard least squares estimation of the average magnetization of a seamount is generally regarded as unsatisfactory the reason for its poor performance is i assert due to the strong correlation and uneven magnitudes of the unfitted noise component of the magnetic anomaly least squares estimation depends for its efficiency and freedom from bias upon the statistical independence and common distribution of the random contamination the primary contributor to the unfitted field is the part due to nonuniformity of the magnetic material within the seamount if the magnetic heterogeneities are modeled as a random stationary vector field of known functional form it is possible to calculate the covariance matrix of the magnetic field noise then to the extent that the statistical description of the magnetic sources is valid the correlation can be properly accounted for in the least squares procedure by weighting the observations to form an equilibrated set with random components that are independent and identically distributed the main use of the average magnetization vector is in the determination of the associated paleopole position i show how the least squares estimates of the magnetization vector and its uncertainty are mapped into a confidence region for the pole position application of this theory to a young seamount in the south pacific is highly satisfactory the model stationary vector field chosen for the magnetization is one with isotropic directional behavior and a very short length scale of correlation it is found that the equilibrated residuals are far less correlated than those of the conventional procedure and the misfits are uniformly distributed throughout the equilibrated data the estimated paleopole position is within a few degrees of the north geographic pole which is the expected location because the seamount is geologically young traditional least squares fitting gave a pole at latitude 60 n the 95 confidence zone associated with the paleopole position has semiaxes measuring 16 by 13 and thus the uncertainty is not much larger than those of standard paleomagnetic work

changes in the intermediate water mass formation rates in the global ocean for the last glacial maximum mid holocene and pre industrial climates 1 the paleoclimate version of the national center for atmospheric research community climate system model version 3 ncar ccsm3 is used to analyze changes in the water formation rates in the atlantic pacific and indian oceans for the last glacial maximum lgm mid holocene mh and pre industrial pi control climate during the mh ccsm3 exhibits a north south asymmetric response of intermediate water subduction changes in the atlantic ocean with a reduction of 2 sv in the north atlantic and an increase of 2 sv in the south atlantic relative to pi during the lgm there is increased formation of intermediate water and a more stagnant deep ocean in the north pacific the production of north atlantic deep water nadw is significantly weakened the nadw is replaced in large extent by enhanced antarctic intermediate water aaiw glacial north atlantic intermediate water gnaiw and also by an intensified of antarctic bottom water aabw with the latter being a response to the enhanced salinity and ice formation around antarctica most of the lgm intermediate mode water is formed at 27 4 29 0 kg m3 while for the mh and pi most of the subduction transport occurs at 26 5 27 4 kg m3 the simulated lgm southern hemisphere winds are more intense by 0 2 0 4 dyne cm2 consequently increased ekman transport drives the production of intermediate water low salinity at a larger rate and at higher densities when compared to the other climatic periods

leakage from inclined porous reservoirs we investigate the effect of localized leakage on the storage of buoyant fluids in inclined porous reservoirs with application to the geological storage of co 2 we find that once the current has propagated some distance beyond the point of leakage its profile becomes steady in time save for the nose which advances at a constant speed crucially this steady state implies that the efficiency of storage defined as the instantaneous proportion of the injected fluid that does not leak tends to a finite value this contrasts with previous studies of localized leakage in horizontal reservoirs which found that the efficiency of storage tends to zero at late times we analyse the steady state efficiency and the time scales of evolution for a leakage point located either upslope or downslope of the injection point using analytical and numerical methods these findings are verified by model laboratory experiments finally we consider the implications of our results for the geological storage of co 2 under sloping cap rocks compromised by a fracture or fissure