new global marine gravity model from cryosat 2 and jason 1 reveals buried tectonic structure gravity models are powerful tools for mapping tectonic structures especially in the deep ocean basins where the topography remains unmapped by ships or is buried by thick sediment we combined new radar altimeter measurements from satellites cryosat 2 and jason 1 with existing data to construct a global marine gravity model that is two times more accurate than previous models we found an extinct spreading ridge in the gulf of mexico a major propagating rift in the south atlantic ocean abyssal hill fabric on slow spreading ridges and thousands of previously uncharted seamounts these discoveries allow us to understand regional tectonic processes and highlight the importance of satellite derived gravity models as one of the primary tools for the investigation of remote ocean basins

tidal fluctuations in a leaky confined aquifer dynamic effects of an overlying phreatic aquifer tidal fluctuations in a leaky confined coastal aquifer are damped significantly due to leakage into an overlying phreatic aquifer jiao and tang 1999 presented an analytical solution to a simple model describing this phenomenon their solution assumes that the tidal fluctuations in the overlying phreatic aquifer are negligible i e a static phreatic aquifer here we examine dynamic effects of the overlying aquifer based on a new approximate analytical solution the numerical results indicate that the dynamic effects can be significant for a relatively large leakage and a high transmissivity of the phreatic aquifer

decadal increases of anthropogenic co2 in the subtropical south atlantic ocean along 30 s 1 using high quality data for dissolved inorganic carbon and related properties obtained about 10 years apart 1992 1993 2003 we examined decadal increases of anthropogenic co2 nctcal along 30 s whp a10 section in the subtropical south atlantic significant nctcal was detectable down to an isopycnal surface of 27 3 1000 m water depth averaged nctcal in sub antarctic mode water samw 26 6 27 0 350 700 m was 6 8 1 6 mol kg 1 and that in antarctic intermediate water aaiw 27 1 27 4 700 1200 m was 3 6 1 4 mol kg 1 in samw nctcal was higher by 7 mol kg 1 west of 15 w than east of it while nctcal in aaiw did not show such a distinct east west difference for deep waters significant nctcal was detected in antarctic bottom water at depths greater than 4500 m in the cape basin longitude 2 e 10 e no significant nctcal could be detected for north atlantic deep water nadw we attributed nctcal being higher west of 15 w in samw to differences of water mass distributions and flows from a water column inventory we estimated the uptake rate of anthropogenic co2 over the decade from 1992 1993 to 2003 to be 0 6 0 1 mol m 2 a 1 which is half the rate in the south pacific 1 0 0 4 mol m 2 a 1

direct velocity measurements in the malvinas current we present a set of current meter measurements collected in the southwest atlantic from december 1993 to june 1995 four moorings were set out to monitor the malvinas falkland current at 40 41 s and one mooring was located within the brazil malvinas front area at 38 s the mean flow of the malvinas current has an equivalent barotropic structure whereas the vertical structure of the variable part of the flow is dominated by a barotropic like empirical mode for regions shallower than 2500 m surface intensified which appears as a linear combination of barotropic and baroclinic modes suggesting mode coupling due to the steep topography this mode appears to gradually become nearly exactly barotropic toward shallower depths higher empirical modes bottom intensified and associated with higher frequencies suggest waves trapped by the conjugated effects of topography and stratification the time variability is discussed in terms of along and cross isobath flows the along shelf flow features substantial energy in the 50 to 70 day band there is no evidence of an annual cycle nor of a distinct semiannual cycle but there is a suggestion of significant energy at periods a little shorter 135 days the cross shelf variability is important with a quite clear annual cycle associated with excursions of the subantarctic front its phase coincides with that of the brazil current transport suggesting that annual migrations of the front are predominately determined by the strength of the latter whereas the intensity of the malvinas current would only have marginal impact a conclusion that may not hold at other timescales

tide induced groundwater head fluctuation in a coastal aquifer system with a submarine outcrop covered by a thin silt layer we present an analytical solution of groundwater head response to tidal fluctuation in a coastal multilayered aquifer system consisting of an unconfined aquifer a leaky confined aquifer and a semi permeable layer between them the submarine outcrop of the confined aquifer is covered by a thin silt layer a mathematical model and the analytical solution of this model are given the silt layer reduces the amplitude of the hydraulic head fluctuation by a constant factor and shifts the phase by a positive constant time lag both of which depend on the leakances of the silt layer and the semi permeable layer the time lag is less than 1 5 h and 3 0 h for semi diurnal and diurnal sea tides respectively when the leakance of the semi permeable layer or the silt layer assumes certain special values the solution becomes the existing solutions derived by previous researchers the amplitude of the hydraulic head fluctuation in the confined aquifer increases with the leakance of the silt layer and decreases with the leakance of the semi permeable layer whereas the phase shift of the fluctuation decreases with both of them a hypothetical example shows that neglecting the silt layer may result in significant parameter estimation discrepancy between the amplitude attenuation and the time lag fittings copyright 2007 john wiley sons ltd

numerical modeling of tidal effects on groundwater dynamics in a multi layered estuary aquifer system using equivalent tidal loading boundary condition case study in zhanjiang china this paper presents a numerical modeling study of tidal effects on groundwater dynamics of a multi layered estuary aquifer system in this study to generalize the tidal loading effects on the confined aquifer we used equivalent tidal loading boundary condition based on existing analytical solutions for the confined aquifer in a three dimensional numerical model and then good simulated result was obtained using the numerical model the tide induced groundwater level and confined groundwater discharge dynamics were discussed and the following conclusions were obtained the combined action of sea tide and river tide can enhance the tidal response of groundwater level in the aquifer system especially for the confined groundwater the river tidal effect is more significant in the areas away from coastline although the confined aquifer is separated by a layer of clay from the ocean because of the tidal loading effects the confined groundwater discharge also changes periodically displaying a negative correlation with the tide level fluctuations like the unconfined groundwater discharge using linear functions that express the relationship between the mean confined groundwater flux and sea tide level the confined groundwater flux through the tidal loading boundaries can be approximately estimated when the sea tide level is higher than 4 4 m there would be a risk of seawater intrusion into the confined aquifer in the study area this case study is useful for numerical studying of tidal effects on groundwater resource dynamics in a coastal multi layered estuary aquifer system

tide induced head fluctuations in a confined aquifer with sediment covering its outlet at the sea floor 1 a confined coastal aquifer usually extends under the sea for some distance with its submarine outlet covered by a thin layer of sediment with properties dissimilar from the aquifer previous theoretical studies neglected this outlet capping in this paper an analytical solution is derived for a confined aquifer subject to tidal fluctuations with a leaky boundary condition at the outlet capping for the cases that offshore length of the aquifer and or the leakance of the outlet capping are either zero or infinity existing solutions in literature are obtained it is shown that our analytical solution can also be used to describe the tidal wave propagation in a confined aquifer extending infinitely under a tidal river the full solution agreed well with the observations in a piezometer in the jahe river basin in china 200 m inland from the coastline where the tide induced head fluctuations without delay were observed but cannot be explained using previous analytical and numerical solutions ignoring the effect of the outlet capping the sensitivity analysis showed that the combined actions of the tidal loading and outlet capping lead to complex dependency of the head fluctuation on the outlet capping s leakance when the offshore confined aquifer is short the inland head fluctuation increases with the outlet capping s leakance in this case significant negative phase shift occurs if the leakance is small for offshore aquifer length greater than a threshold value the inland head fluctuations are independent of this length and the outlet capping s leakance

lagrangian circulation of antarctic intermediate water in the subtropical south atlantic this study combines float data from different projects collected between 1991 and 2003 in the south atlantic to describe the flow of antarctic intermediate water aaiw velocity space time averages are calculated for various grid resolutions and with cells deformed to match the bathymetry f h or f h with h being the water depth and h being the thickness of the aaiw layer when judged by the degree of alignment between respective isolines and the resulting average velocity fields the best grid is based on a nominal cell size of 3o latitude by 4o longitude with cell shapes deformed according to f h using this grid objectively estimated mean currents and their associated errors as well as meridional and zonal volume transports are estimated results show an anticyclonic subtropical gyre centred near 36os and spanning from 23o 1 s to 46 1os the south atlantic current meanders from 33os to 46os and shows a mean speed of 9 6 7 8 cm s 1 8 5 sv 3 5 sv 1 sv 1 106 m3 s 1 the northern branch of the subtropical gyre is located between 22os and 32os and flows westward with a mean speed of 4 7 3 3 cm s 1 9 3 sv 3 4 sv evidence of a cyclonic tropical gyre divided in two sub cells is visible on the stream function

holocene coastal environments and processes in subantarctic temperate cold tierra del fuego argentina chile fil bujalesky gustavo gabriel consejo nacional de investigaciones cientificas y tecnicas centro austral de investigaciones cientificas argentina

tide induced ground water flow in deep confined aquifer water elevation variation in rivers can be large due to tides even far away from the coastline for deep confined aquifers the possibility of leakage from rivers is small nevertheless the fluctuation of river elevation can induce a stress change in soil and in turn can induce ground water flow below the present study focuses on the effect of the fluctuation assuming the time scale for consolidation is much larger than that of the ground water the total stress change in the deep confined aquifer affects the water pressure head through deformable soil medium if the subsurface profile contains only one dominant confined aquifer a vertically averaged one dimensional problem with periodic total stress change and constant line pumping is examined the governing equation is a linear diffusion equation with time varying forcing terms laplace transform and fourier transform are invoked the response distribution in space is of the error function type the pumping effect can be superimposed due to linearity away from the loading deeper aquifers rather than those close to the ground surface are affected by the dynamic loading pressure peaks appear earlier for location farther away from the loading field data support the model

double celled subtropical gyre in the south atlantic ocean means trends and interannual changes 1 we present here a study of the mean upper layer structure of the south atlantic subtropical gyre sasg and its modes of variability based on archiving validation and interpretation of satellite oceanographic data sea level anomaly data gravity recovery and climate experiment based mean dynamic topography mdt models reynolds sea surface temperatures and two tide gauge time series from permanent service for mean sea level analysis of the mdts shows that the sasg mean structure is represented by a double cell circulation the southern cell being a narrow quasi zonal strip centered around 33 s its southern limb is limited by the recently discovered saint helena current tristan da cunha current sthc tcc and the north subtropical front around 35 s this system is shown to be well separated from the south atlantic current south subtropical front around 42 45 s a method based on singular spectrum analysis was used to determine the principal modes of variability through the decomposition of the data into band passed data sets the altimeter sea level trend analysis suggests that the sasg pattern is slowly migrating southward and has been growing in amplitude between 1994 and 2006 with local growth rates of 5 10 mm yr occurring in the southern cell flow intensifications in this period 2 3 cm s in the south equatorial current and north brazil undercurrent 3 5 cm s in the benguela current and weakening by 4 5 cm s in the sthc tcc are recorded the altimeter derived sea level trend is coherent with the growing phase of a bidecadal oscillation found from both tide gauges

tidal groundwater level fluctuations in l shaped leaky coastal aquifer system this paper presents an analytical solution to describe tidal groundwater level fluctuations in a coastal leaky aquifer system bounded by water land boundaries that form a right angle referred to as l shaped coastlines the system consists of an unconfined aquifer a confined aquifer and a leaky layer between them previously published analytical solutions that discuss only single aquifer constitute a special case of the new solution when the permeability of leaky layer approaches zero a simple approximate solution without integral is presented error analysis and hypothetical example show that the approximate solution has adequate accuracy for both groundwater level prediction and parameter estimation for an l shaped leaky aquifer system q 2002 elsevier science b v all rights reserved

rock magnetic properties and relative paleointensity stack for the last 300 ka based on a stratigraphic network from the subtropical and subantarctic south atlantic abstract we present a detailed study of natural remanence and rock magnetic properties of eight sediment cores from a south north profile across the subtropical front stf in the south atlantic which previously have been combined into a stratigraphic network based on these measurements we construct a first relative paleointensity rpi stack for the central south atlantic sas 300 covering the last 300 ka the degree of down core homogeneity of magnetic mineral concentration as well as magnetic mineral content and grain sizes vary between all cores and are quantified by high resolution rock magnetic measurements in the cores north of and close to the stf the magnetic remanence is mainly carried by magnetite the cores in the south also contain a high coercive mineral fraction based on a linear model of the sediment matrix we propose to apply principal component analysis pca of natural remanent magnetization nrm anhysteretic and isothermal remanent magnetization arm and irm to determine a homogeneity interval where remanences are only affected by a single environmental signal this reduces lithologic and climatic influence upon the relative paleointensity record for our data set pca indicates that all remanences in the 30 mt to 80 mt demagnetization interval are dominated by a single environmental influence single core rpi estimates are then obtained by normalizing the nrm fraction in this homogeneity interval with respect to either irm arm in the same interval or by by direct averaging we obtain the stack sas 300 which is compared to other paleointensity series such as sint 800 or the rpi records from odp sites 1089 subantarctic south atlantic and 983 gardar drift the detailed documentation of environmental influences combined with the presentation of seven different recordings of the same geomagnetic signal allows to connect southern and northern hemisphere rpi data also with respect to possible common environmental distortions

a two dimensional analytical solution for groundwater flow in a leaky confined aquifer system near open tidal water groundwater in coastal areas is commonly disturbed by tidal fluctuations a two dimensional analytical solution is derived to describe the groundwater fluctuation in a leaky confined aquifer system near open tidal water under the assumption that the groundwater head in the confined aquifer fluctuates in response to sea tide whereas that of the overlying unconfined aquifer remains constant the analytical solution presented here is an extension of the solution by sun for two dimensional groundwater flow in a confined aquifer and the solution by jiao and tang for onedimensional groundwater flow in a leaky confined aquifer the analytical solution is compared with a two dimensional finite difference solution on the basis of the analytical solution the groundwater head distribution in a leaky confined aquifer in response to tidal boundaries is examined and the influence of leakage on groundwater fluctuation is discussed copyright 2001 john wiley sons ltd

intermediate water in the brazil malvinas confluence zone a lagrangian view the subsurface flow within the subantarctic and subtropical regions around the brazil malvinas falkland confluence zone is studied using daily hydrographic and kinematic data from four subsurface floats and a hydrographic section parallel to the south american shelf the float trajectories are mapped against sea surface flow patterns as visible in concurrent satellite sea surface temperature sst images with focus on the november 1994 and october november 1995 periods the unprecedented employment of lagrangian s diagrams enables us to trace the advection of patches of fresh antarctic intermediate water aaiw from the confluence zone into the subtropical region the fresh aaiw consists of a mixture of subtropical aaiw and malvinas current core water within the subtropical gyre these patches are discernible for extended periods and drift over long distances reaching north to 34 s and east to 40 w the cross frontal migration of quasi isobaric floats across the confluence zone from the subtropical to the subantarctic environment is observed on three occasions the reverse process float migration from a subpolar to a subtropical environment was observed once these events were located near 40 s 50 w the site of a reoccurring cold core feature subsurface float and sst data comparison reveals similarities with analogous observations made in the gulf stream rossby 1996 where cross frontal processes were observed close to meander crests the limited number of floats of this study and the complex structure of the brazil malvinas confluence zone however restricts the analysis to a description of two events

tidal dynamics of the water table in beaches tidal motions of the water table height inside a sloping beach are investigated via field measurements and theoretical considerations only the movements forced by the tide are considered so a beach with negligible wave activity was chosen for the field measurements the data show that even in the absence of precipitation the time averaged inland water table stands considerably above the mean sea level also the water table at a fixed point inside the beach is far from sinusoidal even though its variation is forced by an essentially sinusoidal tide this latter effect is due to the boundary condition along the sloping beach face which acts as a highly nonlinear filter the observed behavior of the water table is explained in terms of perturbation extensions to the classical deep aquifer solution one extension deals with the nonlinearity in the interior the other with the boundary condition at the sloping beach face

a two dimensional analytical solution of groundwater response to tidal loading in an estuary a two dimensional transient groundwater flow equation for a confined nonleaky aquifer is solved analytically with an estuary tidal loading boundary condition the amplitude and phase of the tide varies with position and time respectively these variations called the damping coefficient for amplitude and separation constant for phase along the coastline are considered in the analysis the solution presented is more advanced than the traditional one dimensional analytical solution with a one dimensional tidal loading boundary condition the damping coefficient and separation constant in the application study are obtained from the harmonic analysis of the observed tidal level in apalachicola bay florida the analytical solution is compared to a two dimensional finite difference solution a numerical simulation illustrates the response of piezometric head to tidal loading the piezometric head and phase from both solutions match closely the analytical and numerical solutions show that a piezometric head along both sides of the estuary can be predicted given a tidal elevation at the entry of an estuary the fluctuation of piezometric head in response to tidal loading diminishes rapidly inland and diminishes slowly along the coastline of an estuary there are also obvious phase shifts associated with spatial variations as the wave propagates

sea surface temperature fronts in the midlatitude south atlantic revealed by using microwave satellite data 1 the subtropical convergence or frontal zone has been little studied in the central south atlantic ocean despite limited data some work has suggested that this feature exists continuously across the south atlantic here satellite microwave sensed sea surface temperature sst data available from june 2002 are analysed for the existence of frontal gradients in the subtropical to subpolar south atlantic with focus on the central to eastern region the frontal locations and sst gradients in the southwest south atlantic and in the agulhas current retroflection region obtained from this satellite data are consistent with those estimated previously from hydrographic observations evident in the satellite data is pronounced mesoscale variability in subtropical frontal features particularly south of africa and extending west from the agulhas current retroflection to at least the greenwich meridian and in the southwest south atlantic over the central to eastern part of the basin the analysis suggests that there is substantial interannual variability in the strength and latitudinal location of the northern and southern subtropical front as defined by belkin and gordon 1996 some of this variability may be related to shifts in the winds including that in the latitude of the strongest wind stress curl on seasonal scales this central to eastern region is also characterised by variations in the frontal intensity but shifts in the position of regions of strong gradients are less obvious thus the data indicate that there is no continuous subtropical frontal feature across the basin in terms of surface temperature

land atmosphere ocean interactions in the southeastern atlantic interannual variability land atmosphere ocean interactions in the southeastern south atlantic and their connections to interannual variability are examined using a regional climate model coupled with an intermediate level ocean model in austral summer zonal displacements of the south atlantic subtropical high sash can induce variations of mixed layer currents in the benguela upwelling region through surface wind stress curl anomalies near the namibian coast and an eastward shifted sash is related to the first pacific south american mode when the sash is meridionally displaced mixed layer vertically integrated ekman transport anomalies are mainly a response to the change of alongshore surface wind stress the latitudinal shift of the sash tends to dampen the anomalous alongshore wind by modulating the land sea thermal contrast while opposed by oceanic diffusion although the position of the sash is closely linked to the phase of el nino southern oscillation enso and the southern annular mode sam in austral summer an overall relationship between benguela upwelling strength and enso or sam is absent during austral winter variations of the mixed layer ekman transport in the benguela upwelling region are connected to the strength of the sash through its impact on both coastal wind stress curl and alongshore surface wind stress compared with austral summer low level cloud cover change plays a more important role although wintertime sea surface temperature fluctuations in the equatorial atlantic are strong and may act to influence variability over the northern benguela area the surface heat budget analysis suggests that local air sea interactions dominate

hydraulic head response of a confined aquifer influenced by river stage fluctuations and mechanical loading summary the response to river stage fluctuation of a drilled well penetrating a confined aquifer was simulated using a stream aquifer interaction algorithm because the confined aquifer is overlaid by a water table aquifer the algorithm was coupled with formulae used to correct the heads for mechanical loading the coupling of stream aquifer interaction and mechanical loading models was tried for the first time in this study the test site was a drilled well installed on the montalto uffugo aquifer located at the calabria university groundwater test field calabria region south of italy this aquifer comprises a 44 m thick sand bank bounded on bottom and top by clay layers and covered by a 7 m thick sandy conglomerate being adjacent to the mavigliano river overall the head changes caused by a river stage raise represented a contribution of 49 3 57 8 to the total head while mechanical loading accounted for the remaining 50 7 32 2 the loading was triggered by a sequence of short spaced rainfall events lasting for a total of 167 days which caused recharge to the unconfined aquifer thickening the water column by some 3 1 m

seasonal variability of the south equatorial current bifurcation in the atlantic ocean a numerical study abstract in this study a reduced gravity primitive equation ogcm is used to investigate the seasonal variability of the bifurcation of the south equatorial current sec into the brazil current bc to the south and the north brazil undercurrent current nbuc nbc system to the north annual mean meridional velocity averaged within a 2 longitude band off the south american coast shows that the sec bifurcation occurs at about 10 14 s near the surface shifting poleward with increasing depth reaching 27 s at 1000 m in both observations and model the bifurcation latitude reaches its southernmost position in july 17 s in the top 200 m and its northernmost position in november 13 s in the top 200 m the model results show that most of the seasonal variability of the bifurcation latitude in the upper thermocline is associated with changes in the local wind stress curl due to the annual north south excursion of the marine itcz complex as the sec bifurcation latitude moves south north the nbuc tra

determining the length of confined aquifer roof extending under the sea by the tidal method abstract the main task in studying saline intrusion into an aquifer is to determine the position of the saline water freshwater interface for a confined aquifer this position is determined mainly by the roof length of the aquifer extending under the sea this information can be obtained from fluctuations of the groundwater level caused by tidal fluctuations of the sea in this paper a mathematical model of confined groundwater level fluctuations is constructed on the condition that the roof length is finite taking account of the continuity of flow between the inland and offshore aquifers allows a general formula to be calculated for the groundwater level fluctuations in terms of the tidal fluctuations and the length of the confined aquifer under the sea the actual roof length can be computed by comparison of the observed groundwater level fluctuations with those computed by the formula under various assumptions concerning the roof length the method is applied to an aquifer on the beihai peninsula in the guangxi province of china

is there a continuous subtropical front south of africa a 14 3 year series of weekly absolute sea surface height ssh and associated geostrophic velocities is used for a study of the subtropical to subantarctic frontal system in the region south of africa detecting the fronts from surface velocity maxima confirms a two stepped transition in both the southeastern atlantic ocean the northern and southern subtropical fronts nstf sstf and southwestern indian ocean the agulhas front and sstf as proposed previously from hydrographic data an additional front associated with westward flow north of the nstf is indicative of a partial eastern closure of the south atlantic subtropical gyre between 11 e and 17 5 e the role of northwestward propagating agulhas rings in connecting the two fronts explains the varying location the sstf which marks the southern limit of subtropical waters is found continuous from the atlantic to the indian ocean in the time averaged ssh field in the weekly fields however the velocity maximum criterion defining the front is often met at the southern flanks of agulhas rings or agulhas eddies at 12 e 23 e indicating front disruptions such discontinuities suggest that no south atlantic central water is directly advected into the indian ocean instead the eastward limb of the indo atlantic super gyre encompassing the subtropical gyres of both oceans would rest at these longitudes on diffusive processes at the upper levels and possibly be enhanced at depth a schematic diagram of the fronts and their relations to agulhas rings and eddies is proposed

low velocity layers in the northwestern margin of the south china sea evidence from receiver functions of ocean bottom seismometer data abstract the receiver function method was applied to teleseismic recordings of an active source ocean bottom seismometer array in the northwestern margin of the south china sea forward modeling of the receiver functions was used to derive velocity interfaces beneath the stations two main groups of low velocity layers were imaged the first group in the reef area with a thickness of 7 10 km exhibits a seaward uptrend of the buried depth but poor continuity the second group with a thickness of 3 4 km is more continuous along the zhongsha trough the buried depth decreases asymmetrically from the flanks to the rift center a high shear wave velocity layer of 4 0 km s is imaged at the crust bottom beneath the zhongsha trough with thickness of 3 km the average vp vs in the cenozoic sediment is 2 0 3 0 and was affected by high fluid activity induced by intensive faults the vp vs of the crust varies between 1 77 and 1 88 suggesting an intermediate to basic composition under the continental extension together these results suggest a two stage evolution model of the continental crust in the first stage the crust deformed in a ductile manner and thus created considerable shearing structures with high anisotropy that caused the obvious decrease of the shear wave velocity in the second stage the shearing structures connected asymmetrically driven by detachment faults in the upper crust and upwelling of the lower crust the zhongsha trough then formed probably with magmatic underplating due to lithospheric extension or rising of hot mantle materials

origins and variability of the benguela current a subset of the benguela sources and transports best 1992 1993 data is analyzed to study the magnitude and variability of the large scale transports in the area the data consist of inverted echo sounder series and conductivity temperature depth stations the mean 16 month transport values for the upper 1000 m indicate that of the 13 sv northward transport within the benguela current 50 is derived from the central atlantic which from geometry may be chiefly south atlantic water 25 comes from the indian ocean which may be chiefly agulhas water and the remaining 25 may be a blend of agulhas and tropical atlantic water a simple schematic of the transport pattern with a somewhat restricted corridor for agulhas eddies translation is envisioned to the west of the eddy corridor flows the south atlantic source for the benguela current to the east is the agulhas indian ocean source the corridor is breached by south atlantic and indian water as the transient eddy field stirs these water masses

the south atlantic current in this paper we use the historical hydrographic data base for the south atlantic ocean to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the sub tropical front stf and ii the southern current band of the gyre which is called the south atlantic current sac the stf begins in the west in the brazil falkland malvinas confluence zone but at locations at and west of 45 w this front is often coincident with the brazil current front east of 45 w the stf appears to be a distinct feature to at least the region south of africa whereupon it continues into the indian ocean the associated current band of increased zonal speed is the sac which except for one instance is found at or north of the surface stf until indian ocean water from the agulhas retroflection is reached a reversal of baroclinicity in the stf is observed south of a highly saline agulhas ring causing the sac to separate from the stf and turn north into the benguela current zonal flow south of the stf is generally weak and serves to separate the south atlantic and circumpolar currents in the argentine basin the sac has a typical volume transport of 30 sv 1 sv 106m3s 1 in the upper 1000 m relative to a deep potential density surface 4 45 87 kg m 3 and can be as high as 37 sv it is thus comparable to or stronger than the brazil current in the cape basin the transport of the sac is reduced to about 15 sy before it turns north to feed the benguela current in late 1983 this flow was joined by about 8 sv of water from the agulhas current

anticyclonic and cyclonic eddies of subtropical origin in the subantarctic zone south of africa two eddies one anticyclonic and the other cyclonic intersected in the subantarctic zone south of south africa during a hydrographic transect are described using a large set of measurements including full depth hydrography acoustic doppler current profiler velocities biogeochemical tracers air sea fluxes and altimetric sea surface height both eddies have a subtropical origin the anticyclone is an agulhas ring with convected core water of similar to 12 degrees c and swirl velocities of 1 m s 1 it was 9 5 months old when sampled and had crossed the agulhas ridge though sampled in summer it was releasing similar to 200 w m 2 sensible plus latent heat flux to the atmosphere it was observed adjacent to the subantarctic front illustrating the usual encounters of such structures with this front the cyclone marked by pronounced low oxygen and cfc anomalies revealing an origin at the continental slope was 4 5 months old it had swirl speeds of 0 3 m s 1 and was coupled with the anticyclone when observed from their kinematics and water mass properties both structures were found to transport subtropical water down to similar to 900 m the water trapped below this depth being either from the northern subantarctic zone or local water the two structures illustrate the capacity of eddies in the region to transfer subtropical and alongslope water properties into the subantarctic zone

boundary mixing and topographic blocking on the mid atlantic ridge in the south atlantic abstract it is commonly observed in hydrographic sections crossing midocean ridges that the isopycnals on the ridge flanks slope downward toward the crests although the observed vertical scales of isopycnal dipping are not consistent with steady diffusive boundary layers on slopes the cross flank density gradients can nevertheless be caused by diapycnal mixing acting on timescales of several years the corresponding pressure gradients are usually inferred to be associated with cyclonic along flank flows recent observations of southward flow along the highly corrugated western flank of the mid atlantic ridge near 20 s are inconsistent with this conceptual picture however data from seven zonal cross ridge sections and from four meridional along ridge sections were used to analyze the hydrography on the flanks of the mid atlantic ridge between 2 n and 30 s the majority of the hydrographic stations were occupied over deep cross flank canyons which extend over a total length of 90 000 km in the tropica

dynamics of separating western boundary currents abstract in this work pratt and stern s quasigeostrophic 1 layer infinite jet model is connected to a western boundary by a system of two converging boundary currents the model has a piecewise constant potential vorticity structure and the departing jet has a zonal cusplike profile in the ocean interior the relative strengths of the coastal jets can be varied and the coastline can be tilted relative to north the coastline tilt and the coastal current asymmetry cause an alongshore momentum imbalance that creates a spatially damped quasi stationary wave pattern the presence of the boundary favors the long waves in the model which behave fairly linearly in all study cases the effects of the coastline tilt and the coastal current asymmetry are varied to reinforce or cancel each other in the former case a retroflection type of boundary current separation like the one observed in most southern hemisphere western boundary currents is obtained in the latter case a much smoother separation results

seismic imaging of the transitional crust across the northeastern margin of the south china sea abstract crustal structure across the passive continental margin of the northeastern south china sea scs is presented based on a deep seismic survey cooperated between taiwan and china in august 2001 reflection data collected from a 48 hydrophone streamer and the vertical component of refraction reflection data recorded at 11 ocean bottom seismometers along a nw se profile are integrated to image the upper 1 6 2 4 km s lower 2 5 2 9 km s and compacted 3 4 5 km s sediment the upper 4 5 5 5 km s middle 5 5 6 5 km s and lower 6 5 7 5 km s crystalline crust successively the velocity model shows that the thickness 0 5 3 km and the basement of the compacted sediment are strongly varied due to intrusion of the magma and igneous rocks after seafloor spreading of the scs furthermore several volcanoes and igneous rocks in the upper middle crust 7 10 km thick and a high velocity layer 0 5 km thick in the lower crust of the model are identified as the ocean continent transition oct below the lower slope in the northeastern margin of the scs a thin continent nw of the oct and a thick oceanic crust se of the oct in the continental margin of the northeastern scs are also imaged but these transitional crusts cannot be classified as the oct due to their crustal thickness and the limited amount of the volcano the magma and the high velocity layer the extended continent next to the gravity low and a sag zone extended from the sw taiwan basin may have resulted from subduction of the eurasian plate beneath the manila trench whereas the thick oceanic crust may have been due to the excess volcanism and the late magmatic underplating in the oceanic crust after seafloor spreading of the scs

an analytical solution and case study of groundwater head response to dual tide in an island leaky confined aquifer 1 this paper presents an analytical solution of groundwater head response to dual tide fluctuation in the transect of an island leaky aquifer system comprising a confined aquifer and its overlying semipermeable confining layer both layers terminate at the coastlines on two sides of the island solution analysis indicates that the tidal waves from the two sides of the island transect interfere at the middle of the island and the interference decreases to zero as the horizontal length of the aquifer increases to infinity the leakage of the overlying confining layer enhances the landward attenuation of the tidal head fluctuation and shortens the time lag between the head and tide fluctuations the solution agreed well with the observations in eight piezometers in garden island on the continental shelf of western australia reported by trefry and bekele 2004

multiple oscillatory modes of the argentine basin part ii the spectral origin of basin modes in this paper the spectrum of barotropic basin modes of the argentine basin is shown to be connected to the classical rossby basin modes of a flat bottom constant depth rectangular basin first the spectrum of basin modes is calculated for the argentine basin by performing a normal mode analysis of the barotropic shallow water equations then a homotopy transformation is performed that gradually morphs the full bathymetry geometry through a flat bottom configuration into a rectangular basin following the eigenmodes through this transition establishes a connection between most of the basin modes and the classical rossby basin modes of a rectangular geometry in particular the 20 day mode of the argentine basin is identified with the lowest order mode of classical theory sensitivity studies show that the decay rate of each mode is controlled by bottom friction but that it is insensitive to lateral friction lateral friction strongly impacts the oscillation frequency in addition the modes are found to be only slightly sensitive to the presence of a background flow

tide induced groundwater level fluctuation in a u shaped coastal aquifer summary the prediction of groundwater level fluctuation due to tidal waves propagation in coastal aquifers is important for the planning and management of water resources in coastal areas a two dimensional 2 d analytical solution is derived to describe the tidal groundwater fluctuation in an aquifer bounded by three water land boundaries that form a u shaped coastline two opposite sides represent estuary land boundaries on which the amplitude attenuation and phase shift of the tidal movement in the estuary are considered while the third side is an ocean land boundary the effects of wave interaction due to the propagation of oscillating oceanic tides in the cross shore direction inland and the transmission of the two opposite estuarine tides in the along shore direction are investigated three existing head fluctuation solutions can be considered as special cases of the present solution one is for one dimensional flow and the other two are for 2 d flow a transition distance ranging from 10 to 15 times of tidal propagation length along the shoreline can be estimated based on the solution this distance can be used to judge whether the interaction among tides is significant the influences of hydraulic properties on the tidal fluctuations within the aquifer can therefore be assessed quantitatively based on sensitivity analyses one can conclude that the tidal head is most sensitive to the transmissivity and storativity of the aquifer and least to the damping coefficient of tidal amplitude and wave number along the estuary the sensitivities of head fluctuation to the changes of transmissivity and storativity depend on the shoreline length and whether the interaction among waves is significant on the other hand the sensitivities of head fluctuation to the changes of damping coefficient and wave number increase with diagonal distance from the entry of estuary and reach the largest magnitude near the estuary far away seashore

comment on an analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer by jiu jimmy jiao and zhonghua tang

a 350 ky radiolarian record off luderitz namibia evidence for changes in the upwelling regime abstract the study of radiolarian assemblages from core md 962086 provides new information on the variability in the upwelling intensity and origin of upwelled water masses over the past 350 ky in one of the major filamentous regions of the benguela upwelling system bus located off luderitz namibia the use of key radiolarian species to trace the source of upwelled waters and the use of a radiolarian based upwelling index uri to reconstruct the upwelling intensity represent the first use of radiolarians for paleoceanographic reconstructions in the bus these radiolarian based proxies indicate strongest upwelling during marine isotope stages mis 3 5 and 8 which compares well with other studies while during mis 3 and 8 the radiolarian based proxies indicate the influx of waters of southern ocean origin they also point to the increased influence of tropical waters during the lower portion of mis 5 during mis 2 4 and 6 the radiolarian assemblages indicate generally lower upwelling intensities although this signal is complicated by the increased occurrence of organic carbon in the sediments during these intervals during mis 2 there appears to be less of an input of southern ocean waters to the bus although during the also glacial mis 4 and 6 there is evidence for an increased influence of cold antarctic waters the comparison of the results from core md 962086 with other studies in the bus area indicates a non uniform pattern of upwelling intensity and advection of cold southern waters into this system during mis 2 weaker upwelling signaled by the radiolarian based proxy in mis 4 is in contrast to other studies that indicate higher productivity during this time period in general the data show that there is a strong spatiotemporal complexity in upwelling intensity in the bus and that the advection of water into it is not strongly tied to glacial interglacial variations in climate

barotropic and deep referenced baroclinic ssh variability derived from pressure inverted echo sounders pies south of africa 1 the objective of this paper is to evaluate the baroclinic and barotropic components of sea surface height ssh anomalies in the southern ocean and investigates the causes for the weak correlation between hydrographically derived and satellite measured ssh anomalies to this end data obtained by six pressure inverted echo sounders pies deployed south of africa were used to derive baroclinic and barotropic ssh anomalies our results show that the barotropic component accounts for 30 60 of the variability between the jets of the antarctic circumpolar current acc in contrast the jets associated with the major acc fronts are predominantly baroclinic the deep baroclinic component is important in the acc and accounts for the major part of the baroclinic variability the comparison with along track satellite altimetry jason 1 2 shows correlations coefficients of 0 24 0 92 with low values in regions of high barotropic variability the comparison with gridded aviso satellite altimetry generally shows higher correlation coefficients 0 33 0 92 and lower root mean square rms errors compared to the along track product in conclusion the barotropic ssh anomaly plays a major role in this region and has to be accounted for when assimilating ssh into ocean models due to their high baroclinic component the correct representation of the time and space varying acc fronts seems to be crucial for the right ssh anomaly partitioning used for assimilation purposes gridded products namely aviso seems to be more suitable compared to along track products jason 1 2 in representing the variability of ssh anomalies

decadal change of the south atlantic ocean angola benguela frontal zone since 1980 high resolution simulations with a regional atmospheric model coupled to an intermediate level mixed layer ocean model along with multiple atmospheric and oceanic reanalyses are analyzed to understand how and why the angola benguela frontal zone abfz has changed since 1980 a southward shift of 0 05 0 55 latitude decade 1 in the annual mean abfz position accompanied by an intensification of 0 05 to 0 13 k 100 km decade 1 has occurred as ocean mixed layer temperatures have warmed cooled equatorward poleward of the front over the 1980 2014 period these changes are captured in a 35 year model integration the oceanic warming north of the abfz is associated with a weakening of vertical entrainment reduced cooling associated with vertical diffusion and a deepening of the mixed layer along the angola coast these changes coincide with a steady weakening of the onshore atmospheric flow as the zonal pressure gradient between the eastern equatorial atlantic and the congo basin weakens oceanic cooling poleward of the abfz is primarily due to enhanced advection of cooler water from the south and east increased cooling by vertical diffusion and shoaling of the mixed layer depth in the atmosphere these changes are related to an intensification and poleward shift of the south atlantic sub tropical anticyclone as surface winds hence the westward mixed layer ocean currents intensify in the benguela upwelling region along the namibian coast with a few caveats these findings demonstrate that air sea interactions play a prominent role in influencing the observed decadal variability of the abfz over the southeastern atlantic since 1980

sea surface distribution of coccolithophores in the eastern pacific sector of the southern ocean bellingshausen and amundsen seas during the late austral summer of 2001 abstract horizontal distributions of coccolithophores were observed in sea surface water samples collected on the rv polarstern between 27 february and 10 april 2001 in the pacific sector of the southern ocean bellingshausen and amundsen seas these samples were analyzed to gain information about the distribution of coccolithophores in relation to the oceanic fronts of the southern ocean a total of fifteen species of coccolithophores were identified showing cell abundances of up to 67 103 cells l down to 63 s emiliania huxleyi was the most abundant taxon always accounting for more than 85 of the assemblage the second most abundant species was calcidiscus leptoporus with values lower than 7 cell density increases significantly in both the subantarctic and polar fronts 155 and 151 103 cells l respectively decreasing abruptly in the intervening polar frontal zone and to the south of the polar front although temperature at high latitudes is the main factor controlling the biogeographical distribution of coccolithophores at the regional level southern ocean the frontal systems and consequently nutrient distribution play a crucial role

kinematic elements of antarctic intermediate water in the western south atlantic the northward flowing antarctic intermediate water aaiw is a major contributor to the large scale meridional circulation of water masses in the atlantic together with bottom and thermocline water aaiw replaces north atlantic deep water that penetrates into the south atlantic from the north on the northbound propagation of aaiw from its formation area in the south western region of the argentine basin the aaiw progresses through a complex spreading pattern at the base of the main thermocline this paper presents trajectories of 75 subsurface floats seeded at aaiw depth the floats were acoustically tracked covering a period from december 1992 to october 1996 discussions of selected trajectories focus on mesoscale kinematic elements that contribute to the spreading of aaiw in the equatorial region intermittent westward and eastward currents were observed suggesting a seasonal cycle of the aaiw flow direction at tropical latitudes just offshore the intermediate western boundary current the southward advection of an anticyclonic eddy was observed between 5 degrees s and 11 degrees s farther offshore the flow lacks an advective pattern and is governed by eddy diffusion the westward subtropical gyre return current at about 28 degrees s shows considerable stability with the mean kinetic energy to eddy kinetic energy ratio being around one farther south the eastward deeper south atlantic current is dominated by large scale meanders with particle velocities in excess of 60 cm s 1 at the brazil falkland current confluence zone a cyclonic eddy near 40 degrees s 50 degrees w seems to act as injector of freshly mixed aaiw into the subtropical gyre in general much of the mixing of the various blends of aaiw is due to the activity of mesoscale eddies which frequently reoccupy similar positions c 1999 elsevier science ltd all rights reserved

a crustal structure profile across the northern continental margin of the south china sea an ocean bottom seismometer obs geophysical experiment was carried out across the northern continental margin of the south china sea two dimension kinematic ray tracing was used to construct synthetic records and to define the geological model along the obs profile according to the calculation and interpretation of refracted p wave phases the crustal thickness decreases from 22 km obs 1 in littoral area to 8 km obs 15 in deep sea the lower slope structured by volcanism changes sharply in moho depth from 22 to 9 km the volcanoes over the lower slope were markers of ocean continental transition zone a high velocity layer hvl with an average thickness of 4 km was found in the base of the lower crust over the shelf and slope the south china sea was originated by the passive rifting of south china continent and seafloor spreading however geological and geophysical data collected in the northern margin of the south china sea show a small amount of magma intruded into or erupted onto the crust during pull apart and breakup further analysis shows that the hvz in the base of the thinned continental crust was related to magmatism that occurred after the cessation of seafloor spreading of the south china sea magmatism during the crustal extension and breakup is very weak therefore the northern continental margin of the scs is classified as non volcanic passive margin the southern margin of the south china sea has a crust with a steady thickness of 18 24 km which is different from the nor them margin of the south china sea with a gradually thinned crust they constitute an asymmetrically conjugated pair of passive margins c 2001 elsevier science b v all rights reserved

deep penetration seismic soundings across the northern margin of the south china sea twenty reversed two ship expanding spread profiles esps with maximum source receiver offsets of 100 km were collected in three transects across the rifted northern margin of the south china sea source receiver offset versus two way travel time x t data were mapped into the intercept time versus ray parameter p domain and velocity depth solutions were obtained by a combination of sum inversion in the p domain and ray tracing in both the p and x t domains arrivals from the moho were detected on 17 of the esps the depths to moho determined for individual esp interpretations have reproducibilities of 0 1 km to 3 km in most cases the moho depth has been determined to within 1 5 km moho depths determined in this investigation represent a significant improvement over previous estimates of moho along the margin from gravity data variations in present day crustal thickness measured from top of prerift basement to moho are one measure of the amount and nature of the crustal thinning associated with the rifting of continental crust preceding the formation of the adjacent south china sea basin the esp interpretations reveal that across the eastern portion of the south china margin the crust appears to thin more or less continuously toward the continent ocean boundary in the west esp interpretations also show a general trend of seaward crustal thinning but in addition indicate at least two instances of focused localized crustal thinning crustal velocities and the relative proportion of upper crust vp 6 4 km s are used to identify areas of the south china margin with similar and contrasting crustal structures variations in these properties are believed to result primarily from contrasting prerift crustal structure across the margin however magmatic underplating during rifting depth dependent extension and pleistocene igneous intrusions may also have contributed to the variations in present crustal structure reliable information about variations in crustal thickness and velocity structure across and along the south china margin is an important prerequisite to understanding better the nature of the spatially variable rifting processes which dominated the formation of this margin

the dynamical subtropical front 1 the southern ocean subtropical front stf is thought to play a key role in the global climate system theory suggests that the latitude of the stf regulates the volume of saline agulhas leakage into the atlantic ocean from the indian here we use satellite sea surface temperature sst and sea surface height ssh data to study the physical characteristics of the stf water mass boundary we find that the strong currents in this region do not align with the surface water mass boundary therefore we provide a new climatology for these currents which we define as the dynamical stf dstf the dstf is the eastward extension of the western boundary current in each basin and is characterized by strong sst and ssh gradients and no seasonal cycle at the center of each basin it merges with the sub antarctic front on the eastern side of basins the stf surface water mass boundary coincides with a separate region of multiple sst fronts we call this the subtropical frontal zone stfz the fronts in the stfz have a large seasonal cycle and no ssh signature despite lying close to the same water mass boundary the dstf and stfz are completely unrelated we therefore suggest the term stf only be used when referring to the surface water mass boundary when studying the strong currents on the western side of basins the term dstf is more relevant and similarly the term stfz better describes the region of enhanced sst gradients towards the east

an improved technique for reduction to the pole at low latitudes reduction to the pole at low latitudes based on a wiener filtering approach has been improved by introducing a deterministic noise model it is assumed that the noise power is a fixed fraction of the signal power this allows the method to be fully automated further improvement is obtained by requiring the reduced to the pole field to map into the observed field when projected to the geomagnetic latitude of the observed field this is done by iteratively minimizing the difference between the measured field and the reduced to the pole field projected to the geomagnetic latitude of the measured data this results in a reduced to the pole magnetic map that when projected to the geomagnetic latitude of the given data closely matches the measured data the final reduced to the pole field does not show any of the artifacts typical of reduction to the pole at low geomagnetic latitudes the method is demonstrated on a data set from an aeromagnetic survey flown over north central burkina faso west africa

an analytical solution of groundwater response to tidal fluctuation in a leaky confined aquifer an analytical solution is derived to investigate the influence of leakage on tidal response in a coastal leaky confined aquifer system the analytical solution developed here is more general than the traditional solution obtained by ferris 1951 which can be regarded as a special case of the solution presented in this paper this solution is based on a conceptual model under the assumption that the groundwater level in the confined aquifer fluctuates in response to sea tide while that of the overlying unconfined aquifer remains constant this conceptual model is supported by numerous field studies by previous researchers which have demonstrated that the tidal response in an unconfined aquifer may be negligible compared to that in a confined aquifer the leakage has a significant impact on the tidal behavior of the confined aquifer hypothetical studies indicate that both tidal amplitude of groundwater head in the aquifer and the distance over which the aquifer can be disturbed by the sea tide will be considerably reduced because of the existence of leakage this analytical solution is used to investigate the tidal and piezometer data at the chek lap kok airport hong kong special administrative region people s republic of china

on the negative phase shift of groundwater tides near shallow tidal rivers the gouderak anomaly abstract during a site investigation at gouderak the netherlands the observation was made that groundwater tides in several piezometers near the shallow tidal river hollandsche jsse were running ahead of the river tide by more than an hour although the current theory of groundwater flow does not account for this effect the phenomenon can be explained by means of well known elementary mechanisms the superposition principle is adopted to derive formulae for the phase shift and the attenuation in case of a single aquifer covered by an aquitard it is shown that for this simple system the maximum negative phase shift at the river bank amounts to 1 4 radians corresponding to 1 1 2 hour for the semidiurnal tidal component

sea surface temperatures in the equatorial and south atlantic ocean during the last glacial maximum 23 19 ka 1 we used planktic foraminiferal assemblages in 70 sediment cores from the tropical and subtropical south atlantic ocean 10 n 37 s to estimate annual mean sea surface temperatures ssts and seasonality for the last glacial maximum with a modified version of the imbrie kipp transfer function method iktf that takes into account the abundance of rare but temperature sensitive species in contrast to climap project members 1981 the reconstructed ssts indicate cooler glacial ssts in the entire tropical subtropical south atlantic with strongest cooling in the upwelling region off namibia 7 10 c and smallest cooling 1 2 c in the western subtropical gyre in the western atlantic our data support recent temperature estimates from other proxies in the upwelling regions in the eastern atlantic our data conflict with sst reconstructions from alkenones which may be due to an environmental preference of the alkenone producing algae or to an underestimation of foraminiferal ssts due to anomalous high abundances of n pachyderma sinistral

past hydrographic and climatic changes in the subantarctic zone of the south atlantic the pleistocene record from odp site 1090 abstract pleistocene summer sea surface temperatures ssst have been reconstructed on a composite core section recovered in the subantarctic zone of the southern ocean from planktonic foraminifers applying the modern analog technique the composite consists of core ps2489 2 and the sections recovered at odp site 1090 and documents the last 1 83 ma three distinct climatic periods can be identified that mirror the pleistocene development of the southern ocean hydrography cold climatic conditions prevailed at 43 s during glacial as well as during interglacial periods during the early pleistocene 1 83 0 87 ma indicating a northward shift of isotherms that characterize the present day polar front zone by about 7 of latitude evidence shows a strong linkage between southern ocean and low latitude climate during that interval time between the mid pleistocene revolution ca 0 9 ma and the mid brunhes event ca 0 4 ma we observe higher amplitude fluctuations in the ssst between glacial and interglacial periods corresponding to the temperature range between the present polar front and subantarctic front these climatic variations have been related to changes in the northern hemisphere ice sheets the past 0 4 ma are characterized by strong ssst variations of up to 8 c between glacials and interglacials only during the climatic optima stages 11 3 9 3 7 5 7 1 5 5 and the early holocene ssst exceeded present ssst at the core locality 10 2 c although the carbonate dissolution record exhibits high variability during the pleistocene it can be shown that ssst estimates were not significantly biased the mid brunhes dissolution cycle as well as the mid pleistocene enhanced carbonate preservation appear to belong to a global long term variability in carbonate preservation

three dimensional magnetic structure and genesis of the oceanic crust of the northern south china sea abstract the north continental margin of the south china sea is an area conducive to examining the deep structure tectonic evolution and dynamic mechanisms of this region as there is an influence of oblique magnetization in mid latitude areas on the magnetic data pertaining to this area this study develops and validates an inversion method for magnetic anomalies that accounts for inclination and declination the inversion of the total magnetic intensity t in the northern south china sea was then used to reveal the distribution of magnetic bodies in this area the inversion results show that there is significant tectonic zoning in the area under study with north to south and east to west belts showing a pattern consistent with the main tectonic direction in this area there are also distinct differences between the high magnetic anomaly belt in the continental margin and the magnetic inversion features of the magnetic quiet zone in the south combined with ocean bottom seismology profiles and geothermal data the observed phenomena may be closely related to magmatic underplating activity in the deep crust caused by plate subduction

a stratigraphic network across the subtropical front in the central south atlantic multi parameter correlation of magnetic susceptibility density x ray fluorescence and δ18o records abstract computer aided multi parameter signal correlation is used to develop a common high precision age model for eight gravity cores from the subtropical and subantarctic south atlantic since correlations between all pairs of multi parameter sequences are used and correlation errors between core pairs a b and b c are controlled by comparison with a c the resulting age model is called a stratigraphic network precise inter core correlation is achieved using high resolution records of magnetic susceptibility wet bulk density and x ray fluorescence scans of elemental composition additional 18o records are available for two cores the data indicate nearly undisturbed sediment series and the absence of significant hiatuses or turbidites after establishing a high precision common depth scale by synchronously correlating four densely measured parameters fe ca the final age model is obtained by simultaneously fitting the aligned 18o and records of the stratigraphic network to orbitally tuned oxygen isotope j imbrie j d hays d g martinson a mcintyre a c mix j j morley n g pisias w l prell n j shackleton the orbital theory of pleistocene climate support from a revised chronology of the marine 18o record in a berger j imbrie j hays g kukla b saltzman eds milankovitch and climate understanding the response to orbital forcing reidel publishing dordrecht 1984 pp 269 305 d martinson n pisias j hays j imbrie t c moore jr n shackleton age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy quat res 27 1987 1 29 or susceptibility stacks t von dobeneck f schmieder using rock magnetic proxy records for orbital tuning and extended time series analyses into the super and sub milankovitch bands in g fischer g wefer eds use of proxies in paleoceanography examples from the south atlantic springer verlag berlin 1999 pp 601 633 besides the detection and elimination of errors in single records the stratigraphic network approach allows to check the intrinsic consistency of the final result by comparing it to the outcome of more restricted alignment procedures the final south atlantic stratigraphic network covers the last 400 kyr south and the last 1200 kyr north of the subtropical front stf and provides a highly precise age model across the stf representing extremely different sedimentary regimes this allows to detect temporal shifts of the stf by mapping mn fe it turns out that the apparent stf movements by about 200 km are not directly related to marine oxygen isotope stages

tide induced groundwater level fluctuation in coastal aquifers bounded by l shaped coastlines 1 this paper presents an analytical solution to describe tidal groundwater level fluctuations in an aquifer bounded by two water land boundaries that form a right angle the aquifer configuration can represent the situation of a right angle corner in an island when the tidal boundaries are the same along both boundaries or the estuary situation if the amplitude damps with distance along one boundary river and the amplitude along the other boundary sea does not change spatially the two dimensional flow equation subject to periodic boundary conditions is changed into a time independent elliptic problem using complex transform the elliptic problem is then solved using the green s function method li et al 2000 obtained a nonperiodic solution to the same problem with an additional hypothetical initial condition their solution includes a time dependent integral the solution presented here is a significant improvement over theirs in the sense that the solution is periodic and computationally efficient since the integral involved is independent of time an approximate solution without integral is also derived an error analysis and a case study in hong kong demonstrate that the approximate solution is adequate for most field problems index terms 1829 hydrology groundwater hydrology 1832 hydrology groundwater transport 1899 hydrology general or miscellaneous 3384 meteorology and atmospheric dynamics waves and tides keywords periodic groundwater flow analytical solution coastal aquifer sea tide l shaped coastline

structure and transport of the antarctic circumpolar current and agulhas return current at 40 e hydrographic data are presented from a near meridional section across the agulhas return current the subtropical front and the antarctic circumpolar current acc in the southwest indian sector of the southern ocean the location and characteristics of the fronts are examined and the water masses are defined the agulhas return current emerges as a strong current as far east as 40 e which forms a marked front that is separate from the subtropical front and can be distinguished by a separate water mass comparisons are made with a similar hydrographic section at the greenwich meridian and several notable differences are found the subantarctic front at the greenwich meridian is a pronounced feature carrying a large proportion of the geostrophic transport of the acc on the southwest indian section however the subantarctic front is merged with the polar front at 48 s where the flow associated with the acc is concentrated geostrophic calculations show a large volume transport 84 to 103 sverdrup 1 sv 106 m3 s 1 associated with the agulhas return current at 40 s this is quite separate from the transport of the acc which totals 138 sv south of the subantarctic zone and the crozet plateau or 150 sv including flow in the subantarctic zone the transport of the acc out of the south atlantic sector appears to be higher than the transport into the south atlantic sector at drake passage with the extra transport most probably carried by upper layer and intermediate waters eddies are seen to be an important feature of the subantarctic zone where they help to modify the water masses antarctic intermediate water appears in two forms a saline 34 4 indian ocean variety and a fresh 34 2 atlantic ocean variety the atlantic variety is freshest at the polar front and occupies the southern half of the subantarctic zone within the eddies in the central subantarctic zone there is interleaving between these two forms of antarctic intermediate water north atlantic deep water is unable to cross the southwest indian ridge but can pass south of the crozet plateau in the form of circumpolar deep water which is slightly more saline 34 75 than at drake passage 34 73

tide induced groundwater fluctuation in a coastal leaky confined aquifer system extending under the sea this paper presents the analytical solution of groundwater response to tidal fluctuation in a coastal multilayer aquifer system consisting of a leaky confined aquifer a semipermeable layer and an unconfined aquifer the semipermeable layer or the roof of the leaky confined aquifer extends under the sea comparisons are made with solutions derived previously which considered only a single aquifer zero extension of the roof or infinite roof length and demonstrate that the previous solutions are special cases of the solution presented here a hypothetical example is used to discuss the impact of the dimensionless roof length dimensionless leakage and tidal efficiency on the groundwater level fluctuations in the inland part of the confined aquifer the fluctuation decreases significantly with the roof length when the roof length is small but is insensitive to the change of roof length when the roof length is greater than a threshold the impacts of leakage from the offshore and inland portions of the confining unit are different leakage from the offshore portion tends to increase the fluctuation of the groundwater level while leakage from the inland portion tends to decrease the fluctuation the fluctuation increases as the tidal efficiency increases this fact is significant only when the roof length is great and leakage is small

seismic structure in the northeastern south china sea s wave velocity and vp vs ratios derived from three component obs data a nearly 500 km long seismic profile with reflective and refractive wide angle ocean bottom seismometer obs data and multi channel seismic mcs data was acquired across the northeastern continental margin of the south china sea scs the s wave crustal structure and vp vs ratios have been obtained based on a previously published p wave model using the software raylnvr modeling of vertical and horizontal component obs data yields information on the seismic crustal velocities lithology and geophysical properties along the obs 2001 seismic profile s wave velocities in the model increase generally with depth but exhibit high spatial variability particularly from the shelf to the upper slope of the northeastern scs margin vp vs ratios also reveal significant lithological heterogeneity dongsha penghu uplift dpu is a tectonic zone with a thicker crust than adjacent areas and a high magnetic anomaly with a vp vs of 1 74 and a p wave velocity of 5 0 5 5 km s the dpu primarily consists of felsic volcanic rocks in the upper crust and is similar to the petrology of zhejiang fujian volcanic provinces which perhaps is associated with a mesozoic volcanic arc the ocean continent transition oct in the northeastern scs is characterized by a thinning continental crust volcanoes in the upper crust and a high velocity layer hvl in the lower crust the s wave velocity and vp vs ratio suggest that the hvl has a mafic composition that may originate from underplating of the igneous rocks beneath the passive rifted crust after the cessation of seafloor spreading c 2009 elsevier b v all rights reserved

major nutrients and dissolved oxygen as indicators of the frontal zones in the atlantic sector of the southern ocean 1 the chemical tracers of the main frontal zones of the atlantic sector of the southern ocean are considered before the beginning of the spring bloom frontal zones are distinguished by lateral gradients of dissolved oxygen phosphate nitrate and silicate during the spring bloom the smoothing of nutrient concentrations on both sides of the fronts weakens lateral gradients of chemical properties the position of surface gradients of nutrients within the subtropical frontal zone stfz does not coincide with the location of temperature and salinity gradients as a result fronts in this region have a stepped character the best chemical indicator of the northern stfz front is the dissolved oxygen gradient which coincides with the temperature and salinity gradients the southern boundary of the stfz is distinguished by the gradient of nitrate the chemical criterion for identifying the subantarctic front is the gradient of oxygen which ranges from 0 5 to 4 0 mol kg 1 per km the polar front is identified by the gradient of silicate 0 56 to 2 78 m per km at the surface the weddell scotia confluence wsc is distinguished not by the temperature and salinity but by chemical parameters the best year round criterion is the lateral gradient of silicate to phosphate atomic ratio which ranges from 25 to 35 other markers of the wsc are the gradients of silicate at the surface oxygen at the upper boundary of the circumpolar deep water and the depths of its location

interaction of the south american monsoon system and the southern westerly wind belt during the last 14 kyr abstract surface currents and sediment distribution of the se south american upper continental margin are under the influence of the south american monsoon system sams and the southern westerly wind belt swwb both climatic systems determine the meridional position of the subtropical shelf front stsf and probably also of the brazil malvinas confluence bmc we reconstruct the changing impact of the sams and the swwb on sediment composition at the upper rio grande cone off southern brazil during the last 14 cal kyr bp combining sedimentological geochemical micropaleontological and rock magnetic proxies of marine sediment core geob 6211 2 sharp reciprocal changes in ferri and paramagnetic mineral content and prominent grain size shifts give strong clues to systematic source changes and transport modes of these mostly terrigenous sediments our interpretations support the assumption that the sams over se south america was weaker than today during most of the late glacial and entire early holocene while the swwb was contracted to more southern latitudes resembling modern austral summer like conditions in consequence the stsf and the bmc were driven to more southern positions than today s favoring the deposition of fe rich but weakly magnetic la plata river silts at the rio grande cone during the mid holocene the northern boundary of the swwb migrated northward while the stsf reached its northernmost position of the last 14 cal kyr bp and the bmc most likely arrived at its modern position this shift enabled the transport of antarctic diatoms and more strongly magnetic argentinean shelf sands to the rio grande cone while sediment contributions from the la plata river became less important during the late holocene the modern el nino southern oscillation set in and the sams and the austral tradewinds intensified causing a southward shift of the stsf to its modern position this reinforced a significant deposition of la plata river silts at the rio grande cone these higher magnetic silts with intermediate fe contents mirror the modern more humid terrestrial climatic conditions over se south america

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

eastward propagating decadal temperature variability in the south atlantic and indian oceans the origin and structure of eastward propagating decadal temperature variability in the south atlantic and indian oceans are investigated by using long term output of coupled general circulation model composite analysis during the warm southwest indian ocean swio years shows that decadal temperature anomalies in the swio region originate in the south atlantic and are associated with density anomalies since the density anomalies propagate at the speed of a few cm s 1 slower than the speed of the background eastward antarctic circumpolar current and exhibit a surface intensified equivalent barotropic structure the eastward propagation of the density anomalies may be attributed to quasi stationary oceanic rossby waves the density anomalies are also accompanied with anomalous ekman pumping indicating an important contribution from the overlying atmospheric variability the role of atmospheric variability is further examined by evaluating the mixed layer heat balance it is found that the warm temperature anomalies in the south atlantic are due to anomalous entrainment and meridional advection these results suggest that the atmospheric variability plays an important role through the ocean mixed layer in generating the eastward propagation of decadal temperature variability from the south atlantic besides the internal ocean variability as suggested in previous studies

upper ocean temperature and salinity sections in the south atlantic in 1911 hydrographic cruises conducted in july october 1911 by the fram the deutschland and the mowe and in january february 1911 by the stephan provide a survey of the upper south atlantic subtropical gyre during the cold season and of the equatorial atlantic the data accuracy is not as high as in more recent surveys in particular the depth of the measurement is not known precisely the fram temperature is only good to within 0 10 c accuracy and salinity to within 0 02 the south atlantic cold season stations often present a 100 m or thicker surface mixed layer overlaying a thermocline with maximum vertical gradient increasing from the southwest to the northeast a layer of minimum vertical temperature gradient of 0 01 c m 1 at a temperature close to 13 c is embedded in the upper thermocline between 40 w and 20 w on the southern section of the fram 30 s to 35 s this defines a mode water at a density 26 60 close to the surface density of deep mixed layers offshore of the brazil current found between 34 s and 39 21 s but which is warmer and saltier 14 9 c 35 70 the 1911 t s characteristics in the subtropical south atlantic thermocline present little zonal variations with the warmest saltiest water on isopycnal surfaces found in the southwestern portion of the survey and the coldest freshest waters near namibia the 1911 south atlantic surface waters are much colder than the average situation in recent decades average of 0 82 c and are a little fresher 0 04 than the hydrographic climatology for that season in the subtropical gyre the isopycnals were probably deeper in 1911 than in 1926 except in the southwestern corner and the slope of the t s relationship was larger in 1911 than in 1925 1926 with warmer and saltier waters in the upper thermocline above 26 6 26 4 and fresher and cooler waters in the lower thermocline on the other hand t s characteristics in the equatorial thermocline are comparable in 1911 and 1926 both surveys present water masses which are colder and fresher on isopycnal surfaces than the surveys in the 1960s

tidal wave propagation in a coastal aquifer effects of leakages through its submarine outlet capping and offshore roof summary this paper considers a leaky aquifer system comprising an unconfined aquifer a confined aquifer and a confining layer the aquifer s roof the unconfined aquifer terminates at the coastline the confined aquifer and its roof extend under the sea for a certain distance the aquifer s submarine outlet is covered by a thin layer of sediment referred to as the outlet capping hereafter with properties dissimilar to the aquifer previous studies either neglected the leakage through the aquifer s roof or the outlet capping this paper considers both effects and gives an analytical solution to describe the tide induced head fluctuation in the aquifer system for aquifers with zero or infinite offshore length or with impermeable roof or outlet capping or without the outlet capping existing solutions in the literature are obtained we defined the threshold value for the offshore aquifer length which was found to be less than 5 km for typical coastal aquifer systems for an aquifer with its offshore length greater than the threshold the inland head fluctuation becomes insensitive to variations of this length and the outlet capping s leakance the leakage through the offshore roof decreases the threshold value when the offshore confined aquifer is short the inland head fluctuation increases with the outletcapping s leakance in this case negative phase shift occurs near the coastline only for aquifers with small leakages through the offshore roof and the outlet capping in general