deep seismic structure of the kaapvaal craton the kaapvaal craton is remarkable for the intensive jurassic cretaceous kimberlite magmatism there are indications that the hot spot heating of the upper mantle in southern africa continued in the cenozoic however surface wave data in spite of their sensitivity to temperature failed to provide any evidence of thermal agitation at depths less than 350 km beneath the kaapvaal craton bloch et al 1969 we investigated the s velocity structure in the depth range of the mantle transition zone with the aid of teleseismic p to s converted phases our analysis suggests that a layer of anomalously low s velocity is present in the 370 470 km depth interval beneath the kaapvaal craton the anomalous layer is most likely of thermal origin its upper boundary may separate the deep mantle root of the craton from the underlying mantle the anomaly could arise beneath the craton already in the mesozoic and melting within this layer could contribute to the kimberlite magmatism

injection and thermal breakthrough in fractured geothermal reservoirs lbl 12698 preprint submitted to the journal of geophysical research injection and thermal breakthrough in fractured geothermal reservoirs gudmundur s bodvarsson and chin fu tsang may 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info division ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

assessing the reliability of magnesium in foraminiferal calcite as a proxy for water mass temperatures though many studies on the mg contents in the calcitic tests of foraminifers exist the processes controlling its uptake are still a matter of debate laboratory cultures offer an excellent opportunity to reveal these mechanisms the mg concentrations within single chambers of the planktic foraminifer globigerinoides sacculifer brady maintained under controlled laboratory conditions were measured 1 at variable temperatures 19 5 29 5 c and constant salinity and 2 at variable salinity 22 45 and constant temperature the experimental results suggest that under natural conditions temperature is the leading mechanism controlling the mg ca ratio temperature and magnesium are related proportionally a temperature increase of ca 10 c gives rise to an increase of the magnesium concentrations of ca 130 drastic unnatural salinity changes dominate the effects of temperature a 110 change in the mg ca ratio was observed when salinity was elevated or reduced by more than ca 10 specimens which underwent gametogenesis reveal significantly higher mg concentrations than specimens that did not release gametes partition coefficients for mg in foraminiferal calcite are orders of magnitude lower than values from inorganically precipitated calcite when comparing observed mg ca ratios of foraminiferal tests with predicted mg ca ratios calculated according to empirical equations it becomes evident that foraminiferal tests are undersaturated with respect to mg for the water temperature they have experienced apparently foraminifers are capable of controlling their mg concentration the physiological processes presumably responsible for such depressed mg ca ratios appear to be temperature controlled as deduced from the close relationship of the observed mg ca ratios and water temperature this study demonstrates that variations in temperature and salinity are definitely reflected in the mg content of foraminiferal tests magnesium may thus serve as a paleo proxy for past surface water temperatures as long as postdepositional changes and salinity variations are of subordinate importance or can be excluded

distribution patterns of live planktic foraminifers as related to regional hydrography and productive systems of the mediterranean sea abstract distribution patterns of live planktic foraminifers are examined at two times of the year late summer and late winter through horizontal plankton towing along a nw se transect across the west and east mediterranean basins and in the alboran sea french oceanographic cruises vicomed i ii and iii respectively foraminiferal production is significantly different in the two sampling periods and across the west and east mediterranean foraminiferal density is higher in winter than summer e g in the western basin 3700 specimens 1000 m3 in winter against 200 600 specimens 1000 m3 in summer the production averaged for the two sampling sets is higher in the western basin than in the eastern one however in late summer peaks of maximal production are observed in the central mediterranean strait of sicily and ionian basin 1000 to 2000 specimens 1000 m3 where the assemblages are dominated by globigerinoides ruber rosea and g ruber alba in the mediterranean sea frontal regions and semipermanent eddies which are essentially controlled by regional hydrography represent a significant portion of the regional production they also elicit a higher diversity of species their influence is observed in summer as well as in winter at the end of summer the rather shallow mixed layer hosts spinose symbiont bearing species such as g ruber alba g ruber rosea o universa and g trilobus at that season in the western basin the nutrient content of the mixed layer is generally low and the surface layer is rapidly nutrient depleted summer foraminiferal production remains low at the surface with respect to the winter production in the eastern basin late summer and autumn correspond to the biological spring summer foraminiferal production in surface waters is higher than in winter but standing crops are lower than in the western basin for the same species at the same period in summer however frontal structures and eddies are generally better developed than in winter in some particular cases frontal boundaries in the western basin eddies south of cyprus nutrients from intermediate layers can be upwelled through isopycnal or diapycnal mixing to the photic zone and allow for secondary blooms in the western basin these blooms favour the development of grazers at depth globorotalia truncatulinoides g inflata south of cyprus in the eastern basin oligotrophic conditions promote the development of heterotrophic organisms and predatory foraminifers have higher standing stocks g ruber alba g ruber rosea in winter the break down of the thermocline combined with deep turbulent mixing in the northwestern basin and the deepening of the mixed layer in the alboran sea and along the north african coast result in increased phytoplankton biomass and favour reproduction and proliferation of species such as g truncatulinoides or g inflata our observations indicate that the geographic and depth distribution of live foraminiferal species cannot be entirely explained by the general temperature and salinity differences among the different mediterranean basins but that they are strongly related to regional hydrographic patterns hydrography controls the seasonality and depth of the turbulent mixing which differ between the western and the eastern basins the depth of the mixed layer and its seasonal stratification and the strength of the pycnocline nutrient supply and primary production are mostly regulated by these dynamics one may therefore expect that the species assemblages on the sea floor and in deep sea cores will also correlate to the various hydrographic parameters of the overlying water masses

solar forcing of nile discharge and sapropel s1 formation in the early to middle holocene eastern mediterranean we present high resolution records for oxygen isotopes of the planktic foraminifer globigerinoides ruber 18oruber and bulk sediment inorganic geochemistry for holocene age sediments from the southeast mediterranean our 18oruber record appears to be dominated by nile discharge rather than basin scale salinity temperature changes nile discharge was enhanced in the early to middle holocene relative to today the timing of the long term maximum in nile discharge during the early holocene corresponds to the timing of maximum intensity of the indian ocean influenced southwest indian summer monsoon sim this coincidence suggests a major influence of an indian ocean moisture source on nile discharge in the early to middle holocene while presently the atlantic ocean is the main moisture source nile discharge was highly variable on multicentennial time scale during the early to middle holocene being strongly influenced by variable solar activity this solar driven variability is also recorded in contemporaneous sim records however not observed in an atlantic ocean derived west african summer monsoon record from the holocene this supports the hypothesis that the indian ocean moisture source predominantly controlled nile discharge at that time solar driven variability in nile discharge also influenced paleoenvironmental conditions in the eastern mediterranean bulk sediment ba al and v al used as indicators for export productivity and redox conditions respectively varied both in response to solar forcing on multicentennial time scales we suggest that changes in nile discharge on these time scales have been concordant with nutrient inputs to and shallow ventilation of the eastern mediterranean

instantaneous dynamics of the cratonic congo basin understanding the formation mechanisms of cratonic basins provides an examination of the rheological compositional and thermal properties of continental cratons however these mechanisms are poorly understood because there are few currently active cratonic basins one cratonic basin thought to be active is the congo basin located in equatorial africa the congo basin is coincident with a large negative free air gravity anomaly an anomalous topographic depression and a large positive upper mantle shear wave velocity anomaly localized admittance models show that the gravity anomaly cannot be explained by a flexural support of the topographic depression at the congo we analyze these data and show that they can be explained by the depression of the congo basin by the action of a downward dynamic force on the lithosphere resulting from a high density object within the lithosphere we formulate instantaneous dynamic models describing the action of this force on the lithosphere these models show that the gravity and topography of the congo basin are explained by viscous support of an anomalously dense region located at 100 km depth within the lithosphere the density anomaly has a magnitude within the range of 27 60 kg m 3 and is most likely compositional in origin our models do not provide a constraint on the lithospheric viscosity of the congo craton because the shallow location of the anomaly ensures strong coupling of the anomaly to the surface regardless of viscosity structure

thermal drawdown and late stage seismic slip fault reactivation in enhanced geothermal reservoirs late stage seismic slip in geothermal reservoirs has been shown as a potential mechanism for inducing seismic events of magnitudes to 2 6 as late as two decades into production we investigate the propagation of fluid pressures and thermal stresses in a prototypical geothermal reservoir containing a centrally located critically stressed fault from a doublet injector and withdrawal well to define the likelihood timing and magnitude of events triggered by both fluid pressures and thermal stresses we define two bounding modes of fluid production from the reservoir for injection at a given temperature these bounding modes relate to either low or high relative flow rates at low relative dimensionless flow rates the pressure pulse travels slowly the pressure driven changes in effective stress are muted but thermal drawdown propagates through the reservoir as a distinct front this results in the lowest likelihood of pressure triggered events but the largest likelihood of late stage thermally triggered events conversely at high relative non dimensional flow rates the propagating pressure pulse is larger and migrates more quickly through the reservoir but the thermal drawdown is uniform across the reservoir and without the presence of a distinct thermal front and less capable of triggering late stage seismicity we evaluate the uniformity of thermal drawdown as a function of a dimensionless flow rate qd that scales with fracture spacing s m injection rate q kg s and the distance between the injector and the target point l qd qs2 l this parameter enables the reservoir characteristics to be connected with the thermal drawdown response around the fault and from that the corresponding magnitude and timing of seismicity to be determined these results illustrate that the dimensionless temperature gradient adjacent to the fault dtd dxd is exclusively controlled by the factor qd more significantly this temperature gradient correlates directly with both the likelihood and severity of triggered events enabling the direct scaling of likely magnitudes and timing to be determined a priori and directly related to the characteristics of the reservoir this dimensionless scaling facilitates design for an optimum qd value to yield both significant heat recovery and longevity of geothermal reservoirs while minimizing associated induced seismicity

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

microdistribution of mg ca sr ca and ba ca ratios in pulleniatina obliquiloculata test by using a nanosims implication for the vital effect mechanism the mg ca ratio within foraminiferal calcareous tests shells is widely used to reconstruct past seawater temperature however recent studies reported that the organic components within a test affect the mg ca distribution in this study we have measured the mg ca sr ca and ba ca ratios within the planktonic foraminifera pulleniatina obliquiloculata by using a nanosims secondary ion mass spectrometer sims which has excellent spatial resolution 1 m and allows us to compare the distribution of chemical compositions with that of the organic components element compositions show banding distributions composed of alternately higher and lower values of those elemental ratios the mg ca ratios previously considered to be mainly controlled by calcification temperature show larger variations than the values expected from the seawater temperature at the habitat depth of p obliquiloculata comparison of the elemental distribution with the test microstructure reveals that the bands of high mg ca and sr ca ratios correspond with layers of the organic components such coincidence suggests that the organic components strongly affect the mg ca and sr ca ratios within a test in spite of the heterogeneous distribution temperature estimated from the averaged mg ca ratio within a test is consistent with seawater temperature at the habitat depth of p obliquiloculata indicating that whole mg ca ratio of foraminiferal test may be useful as paleotemperature proxy in contrast to the mg ca ratio the heterogenity in ba ca ratio which previously has been considered to be mainly controlled by the ambient seawater composition is not fully matched with the layers of the organic compositions although the organic components concentrate ba other unknown factors appear to also cause heterogenity in ba incorporation

long and short term carbon fluctuations in the eastern mediterranean during the late holocene a high resolution record of carbon isotope changes during the late holocene was obtained in core ga 112 from the easternmost mediterranean over the past 3600 yr a gradual 13 c depletion trend shown by both planktonic and benthic foraminifera corresponds to a global rise in atmospheric co 2 the global and local trends suggest that aridification and biomass destruction in the nile basin played a major role in the global co 2 rise in the late holocene superimposed on the general 13 c trend are four mirror image cycles in 13 c of planktonic and benthic foraminifera higher planktonic 13 c values reflect periods of high productivity off the coast of israel simultaneously decrease in the benthic 13 c values occurred because of degradation of higher organic matter fluxes to the sediment therefore large differences between the two records indicate periods of high productivity the eastern mediterranean productivity fluctuations respond to a periodical replenishment of nutrients to the mixed layer via nile runoff historical data of the nile flood fluctuations for the past 1400 yr show a remarkable coincidence between high and low nile floods and high and low eastern mediterranean productivity levels which are correlated with the periodic monsoonal activity over the nile headwaters

factors controlling the fluoride content of planktonic foraminifera an evaluation of its paleoceanographic applicability abstract this work is an assessment of the effects of seawater salinity and temperature on the incorporation of fluoride into calcitic shells of planktonic foraminifera and of the subsequent modification of shell chemistry by postdepositional dissolution a strong correlation between the fluoride content of most planktonic species and their calcification depth was observed deeper calcifying foraminifera have lower fluoride content and heavier 18o composition perhaps suggesting a temperature control on the partition coefficient however species deviations from this general trend and the absence of correlation between fluoride and sea surface temperature within an individual species suggest that the coprecipitation of fluoride in foraminiferal calcite is more strongly controlled by biological processes rather than by simple chemical relationships foraminiferal fluoride shows weak or no correlation with sea surface salinity core top planktonic foraminifera from the eastern equatorial atlantic sierra leone rise show a substantial decrease of fluoride and to a lesser extent mg content with increasing water depth 2931 5104 m these decreasing trends with depth are attributed to selective dissolution i e removal of the more dissolution susceptible fraction with a different chemical composition than the residual a process which previously has been suggested to account for variations in the isotopic composition of planktonic foraminifera these findings indicate that foraminiferal fluoride cannot serve as a reliable tracer of oceanic paleo temperature or salinity it is possible however that fluoride may be useful for the study of dissolution in deep sea sediments

frozen and active seismic anisotropy beneath southern africa 1 p receiver functions from 23 stations of the sase experiment in southern africa are inverted simultaneously with sks waveforms for azimuthal anisotropy in the upper mantle our analysis resolves the long standing issue of depth dependence and origins of anisotropy beneath southern africa in the uppermost mantle we observe anisotropy with a nearly e w fast direction parallel to the trend of the limpopo belt this anisotropy may be frozen since the archean at a depth of 160 km the fast direction of anisotropy changes to 40 and becomes close to the recent plate motion direction this transition is nearly coincident in depth with activation of dominant glide systems in olivine and with a pronounced change in other properties of the upper mantle another large change in the fast direction of anisotropy corresponds to the previously found low s velocity layer atop the 410 km discontinuity

seasonal variability of the mixed layer depth in the mediterranean sea as derived from in situ profiles a new 0 5 resolution mediterranean climatology of the mixed layer depth based on individual profiles of temperature and salinity has been constructed the criterion selected is a threshold value of temperature from a near surface value at 10 m depth mainly derived by a method applied on the global de boyer montegut et al 2004 dbm04 with respect to dbm04 the main differences reside in the absence of spatial interpolation of the final fields and in the improved spatial resolution these changes to the method are necessary to reproduce the mediterranean mixed layer s behavior in the derived climatological maps the most relevant features of the basin surface circulation are reproduced as well as the areas prone of the deep water formation are clearly identified finally the role of density in the definition of the mixed layer s differing behaviors between the oriental and the occidental regions of the basin is presented

cenozoic deformation of the south african plateau namibia insights from planation surfaces abstract passive margins and associated inland areas display complex vertical displacements that have been abundantly described offshore but much less so onshore due to erosion planation surfaces are ubiquitous markers inland that can be used as a proxy both climatic conditions and changes in vertical displacements induced by both short faults and long tilting flexure wavelength deformations we propose 1 a synthetic typology of the planation surfaces driven by a genetic process weathering versus mechanical erosion and 2 a method to use these surfaces to map short and long wavelength deformations this methodology was applied to the namibian margin and inland plateau to quantify the cenozoic deformation the results show that the namibian margin was affected by bulging during the oligocene and by an e w to nw se extension during the late miocene and pliocene the bulge is parallel to the shoreline with a wavelength of 300 km and an amplitude up to 500 m after investigating the available deformation processes we propose that an increase in the spreading rate along the mid oceanic ridge during the oligocene generated this bulging the vertical displacement is partially maintained afterwards via isostasy because of mass loss generated by scarp retreat a minimum average rate of scarp retreat of 5 km myr was calculated which is high compared to the rates estimated in other places in the world we ascribe this high value to the prior intense weathering period indeed the alteration largely degraded the bedrock and facilitated the formation of the subsequent scarp this study also reveals that the high reliefs of the damara domain existed before the cenozoic induced by a reactivation of the damara structures

the characterisation of saharan dusts and nile particulate matter in surface sediments from the levantine basin using sr isotopes abstract the provenance of sediments within the levantine basin of the eastern mediterranean was studied using 87 sr 86 sr isotopic ratios together with major elements measurements were made on the detrital fraction of surface sediments and the two most important sources of detrital matter to the region saharan dust was characterised by an 87 sr 86 sr isotopic ratio in the range 0 7160 0 7192 there was a small systematic decrease in 87 sr 86 sr from west to east which is interpreted as due to a change in the balance of aeolian source material the nile particulate matter had a 87 sr 86 sr isotopic ratio in the range 0 7057 0 7071 87 sr 86 sr isotopic signatures together with sr concentration were used to calculate the contributions made by saharan dust and nile particulate matter to the surface sediments of the levantine basin it was shown that nile derived sediment was dispersed widely across the levantine basin enabling the area affected by retention of sediment behind the aswan dam to be determined

planktic foraminiferal sedimentation and the marine calcite budget 1 the vertical flux and sedimentation rate of planktic foraminiferal tests are quantified and a global planktic foraminiferal cac0 3 budget is presented test and calcite flux rates are calculated according to the distribution of species obtained from multinet and sediment trap samples modern planktic foraminiferal population dynamics are discussed as a prerequisite for the quantification of the calcite budget highlighting the importance of ecological autecological e g reproduction and biogeochemical conditions that determine the presence or absence of species to complete the open marine particulate caco 3 inventory the contribution of coccolithophores pteropods and calcareous dinophytes is discussed based on the studied regions the global planktic foraminiferal calcite flux rate at 100 m depth amounts to 1 3 3 2 gt yr 1 equivalent to 23 56 of the total open marine caco 3 flux the preservation of tests varies on a regional and temporal scale and is affected by local hydrography and dissolution during most of the year off peak periods many tests dissolve above 700 m water depth while settling through the water column with on average only 1 3 of the initially exported caco 3 reaching the deep seafloor pulsed flux events mass dumps of fast settling particles yield a major contribution of tests to the formation of deep sea sediments on average 25 of the initially produced planktic foraminiferal test cac0 3 settles on the seafloor the total planktic foraminiferal contribution of caco 3 to global surface sediments amounts to 0 36 0 88 gt yr 1 32 80 of the total deep marine calcite budget

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

automated cleaning of foraminifera shells before mg ca analysis using a pipette robot the molar ratio of magnesium to calcium mg ca in foraminiferal calcite is a widely used proxy for reconstructing past seawater temperatures thorough cleaning of tests is required before analysis to remove contaminant phases such as clay and organic matter we have adapted a commercial pipette robot to automate an established cleaning procedure the mg cleaning protocol of barker et al 2003 efficiency of the automated nine step method was assessed through monitoring al ca of trial samples geob4420 2 core catcher planktonic foraminifera globigerinoides ruber globigerinoides sacculifer and neogloboquadrina dutertrei from this sample gave mg ca consistent with the habitat range of the three species and 40 60 sample recovery after cleaning comparison between manually cleaned and robot cleaned samples of g ruber white from a sediment core geob16602 showed good correspondence between the two methods for mg ca r 0 93 p 0001 n 27 average al ca in robot cleaned samples was 0 05 mmol mol showing that the samples are cleaned effectively by the robot the robot offers increased sample throughput as batch sizes of up to 88 samples blanks can be processed in 7 h with little intervention

globorotalia truncatulinoides in central western mediterranean sea during the little ice age abstract globorotalia truncatulinoides oscillations have been recorded from different marine sediment cores collected in the central and western mediterranean sea the abundances of this species over the last 500 yrs demonstrates its potential value as bio indicator of particular oceanographic condition during the maunder minimum mm event of the little ice age lia the comparison between the g truncatulinoides abundance patterns of the balearic basin central and south tyrrhenian sea and central and eastern sicily channel allows to highlight a similar response of this species during the mm event in the central western mediterranean sea the ecological meanings of this species and its peculiar high abundance percentages in the total assemblages suggest the development of enhanced vertical mixing conditions during mm winter season with a strong advection of nutrients from the nutrient rich deeper layers and enhances the productivity levels in the mixed layer the intensified vertical mixing could be linked to persistence of an atmospheric blocking event recorded by several authors during the mm

shifting ocean carbonate chemistry during the eocene oligocene climate transition implications for deep ocean mg ca paleothermometry to date no conclusive evidence has been identified for intermediate or deep water cooling associated with the 1 parts per thousand benthic delta o 18 increase at the eocene oligocene transition eot when large permanent ice sheets first appeared on antarctica interpretation of this isotopic shift as purely ice volume change necessitates bipolar glaciation in the early oligocene approaching that of the last glacial maximum to test this hypothesis it is necessary to have knowledge about deep water temperature which previous studies have attempted to reconstruct using benthic foraminiferal mg ca ratios however it appears likely that contemporaneous changes in ocean carbonate chemistry compromised the mg ca temperature sensitivity of benthic foraminifera at deep sites new geochemical proxy records from a relatively shallow core odp site 1263 estimated paleodepth of 2100 m on the walvis ridge reveal that carbonate chemistry change across the eot was not limited to deep sites but extended well above the lysocline critically limiting our ability to obtain reliable estimates of deep ocean cooling during that time benthic li ca measurements used as a proxy for co32 suggest that co32 increased by similar to 29 mu mol kg at site 1263 across the eot and likely impacted benthic foraminiferal mg ca a co32 benthic mg ca relationship is most apparent during the early eot when the overall increase in co32 is interrupted by an apparent dissolution event planktonic d18o and mg ca records suggest no change in thermocline temperature and a delta o 18 seawater increase of up to 0 6 parts per thousand at this site across the eot consistent with previous estimates and supporting the absence of extensive bipolar glaciation in the early oligocene

the influence of dynamically supported topography on estimates of te abstract the effective elastic thickness t e of continental lithosphere can be estimated from the relationship between gravity and topography in the spectral domain two methods have been used one of which depends on the coherence between bouguer gravity anomalies and topography whereas the other uses the transfer function commonly known as the admittance between the free air gravity and topography the two methods give estimates of t e which differ by as much as an order of magnitude in those continental regions where variations in elevation are small this problem has led to much controversy an important concern is the extent to which estimates of t e are affected by dynamically maintained gravity and topography arising from mantle convection and postglacial recovery unlike elastically supported anomalies these processes can generate gravity and topographic long wavelength 500 km anomalies if such anomalies are modelled as being supported by elastic forces the resulting values of t e are overestimated often by a large amount

seasonal changes in species composition numbers mass size and isotopic composition of planktonic foraminifera settling into the deep sargasso sea abstract planktonic foraminifera recovered from six successive sediment trap samples collected over fourteen months at a depth of 3200 m near bermuda show varied responses to seasonal changes in the near surface hydrography these include changes in species composition and within species changes in number of individuals collected per unit time average size and weight of individuals and in oxygen and carbon isotopic composition a total of seventeen species were identified and eleven were sufficiently abundant for isotopic analysis in at least some of the samples the accumulations on the sea floor of some of these species can be expected to contain a strong seasonal component in their oxygen isotopic composition which may be utilized in paleoclimatic and paleo oceanographic reconstructions best suited to this purpose are those species which form their tests in isotopic equilibrium with surface water and whose abundance is confined to a portion of the year only the best examples are pulleniatina o bliguiloculata globigerinoides conglobatus and neogloboquadrina dutertrei globigerinoides ruber is a good estimator of the average surface water temperature because it occurs in rather even abundance throughout the year hastigerina pelagica though very abundant in surface water is practically eliminated even before arrival on the sea floor by partial resorption and structural weakening of the tests during gametogenesis orbulina universa globorotalia truncaltulinoides and globorotalia hirsuta show morphological and istopic evidence for contibnued calcification in deeper water after initial test formation near ther surface globigerina bulloides represents the most striking example of oxygen isotopic disequilibrium with sea water

global climate instability reflected by eastern mediterranean marine records during the late holocene abstract extremely high sediment accumulation rates in the southeastern se mediterranean off israel make this region ideal for high resolution paleoceanographic reconstructions two cores were examined and foraminiferal oxygen and carbon isotope composition as well as physical and geochemical properties of the sediments were used to reconstruct the climatic and environmental changes of the se mediterranean basin during the late holocene 3 6 ka the 18o values of globigerinoides ruber suggest that the freshwater balance changed several times during this time interval humid phases took place between 3 5 3 0 ka bp and 1 7 1 0 ka bp the later was accompanied by enhanced preservation of terrestrial organic matter within the sediment ors event relatively more arid conditions prevailed in this area between 3 0 and 1 7 ka bp during the last millennia at ca 0 8 and 0 27 ka two climatic events occurred which are probably correlative to both the medieval warm period and the cooling global event known as the little ice age respectively a long term slight increase in planktonic foraminiferal 18o values occurs together with a gradual decrease in the 13c values of both g ruber and the benthic foraminifera uvigerina mediterranea this trend is associated with an increase in sedimentation rates ti al ratio magnetic susceptibility and color index of the sediments we suggest that this trend shown by various independent proxies seems to be related to the aridification process that started ca 7 0 ka in the mid low latitude desert belt and the se mediterranean region and continuous until the present the long term 13c decrease shown by surface and bottom water foraminifera reflects a gradual change in the 13c of the dissolved co2 of the entire se mediterranean water column this follows the global co2 rise in the late holocene as a result of the terrestrial biomass destruction during the aridification process moreover the gradual reduction of the vegetation cover in east africa led to an increased erratic flood related sediment flux via the nile river up to the present this is reflected by the general change in the local sediment composition at 3 6 ka the saharan eolian input reached 65 whereas at about 0 3 ka 70 of the se mediterranean sediment was composed of nile particulate matter

topographic asymmetry of the south atlantic from global models of mantle flow and lithospheric stretching the relief of the south atlantic is characterized by elevated passive continental margins along southern africa and eastern brazil and by the bathymetric asymmetry of the southern oceanic basin where the western flank is much deeper than the eastern flank we investigate the origin of these topographic features in the present and over time since the jurassic with a model of global mantle flow and lithospheric deformation the model progressively assimilates plate kinematics plate boundaries and lithospheric age derived from global tectonic reconstructions with deforming plates and predicts the evolution of mantle temperature continental crustal thickness long wavelength dynamic topography and isostatic topography mantle viscosity and the kinematics of the opening of the south atlantic are adjustable parameters in thirteen model cases model predictions are compared to observables both for the present day and in the past present day predictions are compared to topography mantle tomography and an estimate of residual topography predictions for the past are compared to tectonic subsidence from backstripped borehole data along the south american passive margin and to dynamic uplift as constrained by thermochronology in southern africa comparison between model predictions and observations suggests that the first order features of the topography of the south atlantic are due to long wavelength dynamic topography rather than to asthenospheric processes the uplift of southern africa is best reproduced with a lower mantle that is at least 40 times more viscous than the upper mantle

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

effect of lateral viscosity variations in the top 300 km on the geoid and dynamic topography summary we have investigated the impact of lateral viscosity variations lvv in the top 300 km of the mantle on the long wavelength gravitational response of the earth in contrast to the previous studies we demonstrate that the lvv may play a crucial role if a model with imposed plate velocities and partial layering is considered assuming lvv in the top mantle associated with the continental roots and the oceanic asthenosphere we are able to explain a significant portion of the geoid 85 per cent and of the free air gravity data 55 per cent without invoking a complex radial viscosity profile or assuming a lithosphere with an unrealistically low uniform viscosity the best fit to the data is found for models in which mass anomalies located at the boundary between upper and lower mantles reduce the mass flux across the 660 km discontinuity by a factor of 3 these models are characterized by a low average value of viscosity in the asthenosphere below the oceans 10 19 pa s and a large viscosity contrast 100 between the young suboceanic mantle and the deep continental roots the viscosity in the deep upper mantle is found to be around 3 10 20 pa s while a value higher by at least two orders of magnitude is typical for the lower mantle the predicted dynamic surface topography is influenced by the surface plate velocities and its amplitude amounts to a few hundred metres besides investigating the viscosity structures that reflect the different thicknesses of the lithosphere in continental and oceanic regions we have searched for a large scale pattern of lateral viscosity variation in the top 300 km that yields the best fit to the geoid the pattern obtained by this inversion shows a good correlation with the ocean continent distribution and 90 per cent of the geoid and 67 per cent of the free air gravity can be explained

joint seismic geodynamic mineral physical modelling of african geodynamics a reconciliation of deep mantle convection with surface geophysical constraints recent progress in seismic tomography provides the first complete 3 d images of the combined thermal and chemical anomalies that characterise the unique deep mantle structure below the african continent we present a tomography based model of mantle convection that provides an excellent match to fundamental surface geodynamic constraints on internal density heterogeneity that includes both compositional and thermal contributions where the latter are constrained by mineral physics the application of this thermochemical convection model to the problem of african mantle dynamics yields a reconciliation of both surface gravity and topography anomalies to deep seated mantle flow under the african plate over a wider range of wavelengths than has been possible to date on the basis of these results we predict flow in the african asthenosphere characterised by a clear pattern of focussed upwellings below the major centres of late cenozoic volcanism including the kenya domes hoggar massif cameroon volcanicline cape verde and canary islands the flow predictions also reveal a deep seated large scale active hot upwelling below the western margin of africa under the cape verde islands that extends down to the core mantle boundary the scale and dynamical intensity of this west african superplume is comparable to the south african superplume that has long been assumed to dominate the large scale flow dynamics in the deep mantle under africa we evaluate the plausibility of the predicted asthenospheric flow patterns through a comparison with seismic azimuthal anisotropy derived from independent analyses of african shear wave splitting data

effect of diagenesis on the sr o and c isotope composition of late cretaceous mollusks from the western interior seaway of north america evaluating the effects of diagenesis on the isotopic compositions of sr o and c in marine carbonates is critical to their use as proxies in reconstructing information on the salinity temperature and dissolved inorganic carbon of ancient oceans we have analyzed a series of samples of mollusk shells from the baculites compressus zone late campanian of the pierre shale of south dakota samples included outer shell material and septa of cephalopods collected inside and outside concretions preservation was evaluated using light microscopy scanning electron microscopy sem trace element analysis and x ray diffraction all of the material consists of aragonite based on x ray diffraction an sem preservation index pi was established based on comparison of the microstructure of the fossil material with that of modern nautilus excellent preservation pi 5 was characterized by well defined nacreous plates with discrete angular boundaries in contrast samples showing fused nacreous plates with indistinct boundaries were rated poor pi 1 87sr 86sr ratios vary with preservation and average 0 707648 000021 n 10 for excellent preservation pi 5 0 707615 000028 n 5 for good preservation pi 3 0 707404 000074 n 7 for fair preservation pi 2 and 0 707261 000053 n 8 for poor preservation pi 1 these data suggest that as the quality of the preservation declines the mean 87sr 86sr ratio decreases and the standard error of the mean increases oxygen and carbon isotope analyses of the same specimens also show decreases with preservation and 18o 13c and 87sr 86sr are well correlated suggesting that these tracers are all altered as the pi decreases the sr ca ratio increases as preservation decreases indicating that sr is added to the shell material during diagenesis in contrast mg ca shows no trend with preservation if the increasing sr concentration and decreasing 87sr 86sr of the shell material with decreasing preservation represents the addition of sr to the shell during diagenesis we calculate that the added sr had 87sr 86sr ranging from 0 707582 to 0 707032 potential sources of the added sr include older marine carbonates and weathering of volcanic ash layers present in the shale the mechanisms of alteration likely include epitaxial growth of strontianite on the original shell aragonite and isotopic exchange of c and o between alteration fluids and shell carbonate we conclude that sem preservation criteria are effective in screening shell material that records original isotopic values and that variations in sr o and c isotope composition in well preserved material can be used to assess paleoenvironmental parameters such as salinity and temperature our results also indicate that assessing preservation is a critical prerequisite to the determination of numerical ages of shell material using strontium isotope stratigraphy

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

moho depth and crustal composition in southern africa abstract we present new results on structure thickness and composition of the crust in southern africa based on 6300 seismic receiver functions at 85 stations application of hk stacking to the entire sase dataset and use of multi frequency bands improve resolution substantially we observe a highly heterogeneous crustal structure with short wavelength variations in thickness h vp vs ratio composition and moho sharpness which defines 20 blocks that do not everywhere coincide with surface tectonic features in the zimbabwe craton the tokwe block has h 35 38 km and vp vs 1 74 1 79 whereas the thicker crust in the tati block h 47 51 km may be related to deformation of the archean crust along the cratonic margin two distinct crustal blocks with similar crustal thickness 42 46 km but significantly different vp vs ratios are recognized in the limpopo belt extreme values of 1 90 1 94 at the dyke swarms in eastern limpopo and 1 84 at the olifants river dyke swarm and easternmost bushveld intrusion complex bic indicate voluminous magmatic intrusions in the whole crust we find no evidence for magmatic intrusions in the central inferred part of bic where the crust is thick 45 50 km and vp vs is low 1 68 1 70 this thick crustal root may have deflected rising magmas to form the two bic lobes most of central kaapvaal has thin 35 40 km crust and vp vs 1 74 these characteristics are similar to the tokwe block in zimbabwe craton and may indicate delamination of pre existing lower crust which is further supported by a very sharp moho transition the exposed cross section in the vredefort impact crater is non representative of cratonic crust due to shallow moho 34 km and high vp vs 1 80 attributed to shock metamorphism high vp vs 1 76 is typical of the witwatersrand basin and anomalously low vp vs 1 66 1 67 marks the kaapvaal kheis namaqua transition highly heterogeneous crust both in thickness and vp vs ratio is typical of the namaqua natal and cape fold belts

sea surface temperature pattern reconstructions in the arabian sea from throughout the arabian sea for four distinct time intervals 0 ka 8 ka 15 ka and 20 ka with the aim of understanding the history of the indian monsoon and the climate of the arabian sea region this was accomplished through the use of paired mg ca and d 18 o measurements of the planktonic foraminifer globigerinoides ruber by analyzing basin wide changes and changes in cross basinal gradients we assess both monsoonal and regional scale climate changes sst was colder than present for the majority of sites within all three paleotime slices furthermore both the indian monsoon and the regional arabian sea mean climate have varied substantially over the past 20 kyr the 20 ka and 15 ka time slices exhibit average negative temperature anomalies of 2 5 3 5 c attributable in part to the influences of glacial atmospheric co2 concentrations and large continental ice sheets the elimination of the cross basinal sst gradient during these two time slices likely reflects a decrease in summer monsoon and an increase in winter monsoon strength changes in d 18 ow that are smaller than the d 18 o signal due to global ice volume reflect decreased evaporation and increased winter monsoon mixing ssts throughout the arabian sea were still cooler than present by an average of 1 4 ci n the 8 ka time slice these cool ssts along with lower d 18 ow throughout the basin are attributed to stronger than modern summer and winter monsoons and increased runoff and precipitation the results of this study underscore the importance of taking a spatial approach to the reconstruction of processes such as monsoon upwelling

further constraints on the diagenetic influences and salinity effect on globigerinoides ruber white mg ca thermometry implications in the mediterranean sea we analyzed mg ca ratios of the planktonic species globigerinoides ruber white picked from 49 box core samples covering the whole mediterranean sea and 2 core tops from the atlantic ocean over the entire data set we found no significant correlation between mg ca and 18o derived calcification temperatures this lack of correlation is chiefly due to the presence of an early diagenetic mg rich calcite coating which can constitute up to 20 of the total shell calcite in the central and eastern mediterranean basin and result in anomalously high mg ca values and a high scattering in the western mediterranean sea however g ruber mg ca scattering shows smaller amplitude and mg rich calcite remains under the xrd detection limit sem observations indicate that only a few samples are affected by trace amounts of post mortem calcite overgrowths most of this calcite being likely removed during the chemical cleaning for mg ca analyses using core top sediments from the western mediterranean sea we performed an empirical calibration exercise which confirms that g ruber mg ca is not only related to temperature but it is also significantly affected by sea surface salinity this salinity effect is not specific to high salinity environments such as the mediterranean sea since it appears to be coherent with recent results obtained on indo pacific and atlantic surface sediments which suggest that a 1 psu change in sss results in a 1 7 c mg ca temperature bias this sensitivity to salinity is significantly higher than those deduced from culture experiments

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

variations in mg ca and sr ca ratios of planktonic foraminifera caused by postdepositional dissolution evidence of shallow mg dependent dissolution a comparative study has been made of two species of planktonic foraminifera g tumida and g sacculifer in a depth transect on the ontong java plateau western equatorial pacific g tumida tests from core top sediments showed decreasing mg ca 2 65 1 25 mmol mol and sr ca 1 50 1 16 mmol mol ratios with increasing water depth 1600 4400 m while no such variation was found in g sacculifer tests in excess of 355 m average mg ca 3 6 mmol mol sr ca 1 4 mmol mol artificial dissolution of g tumida tests led to a decrease in both mg ca and sr ca but in g sacculifer there was no significant change in the ratios analyses by electron microprobe revealed that mg ca of the inner chamber calcite in g tumida tests was much higher than that of the calcite crust keel whereas sr ca was only slightly elevated there were no consistent spatial differences in either mg ca or sr ca for g sacculifer tests dissolution in the oceans gives rise to the removal of the chamber calcite in g tumida about 30 of the total calcite leaving the keel calcite although g tumida is thought of as a dissolution resistant form the majority of mg ca and sr ca depletion and chamber loss occurs above the lysocline it is also possible that much of the mg enriched gametogenic calcite has been lost by dissolution from g sacculifer above 1600 m mg content has a significant effect on the dissolution susceptibility of planktonic foraminifera calculations show that the saturation horizon for mg rich parts of tests may be elevated by several hundred meters compared with normal calcite

core top calibration of mg ca in tropical foraminifera refining paleotemperature estimation 1 optimal use of mg ca as a paleotemperature proxy requires establishing calibrations for different species of foraminifera and quantifying the influence of dissolution to achieve this goal we have measured mg ca and 18o in a series of tropical and subtropical core tops including four depth transects the ceara rise the sierra leone rise and the rio grande plateau in the atlantic and the ontong java plateau in the pacific focusing on spinose mixed layer dwelling species globigerinoides ruber and globigerinoides sacculifer and nonspinose thermocline dwelling neogloboquadrina dutertrei shell mg ca in g sacculifer is 5 15 lower than in g ruber while n dutertrei mg ca is 49 55 lower than in g ruber this statistically significant offset has allowed us to establish different calibrations for each species multilinear regression analysis was used to develop calibration equations that include a correction term for the dissolution effect on mg ca in foraminiferal calcite presented in this paper are two sets of calibrations one set using core depth as a dissolution correction and another using co32 as a dissolution parameter the calibrations suggest that g ruber is the most accurate recorder of surface temperature while g sacculifer records temperatures below the surface at 20 30 m the depth habitat of n dutertrei is more uncertain owing to the wide range in habitat depths depending on hydrographic conditions but on average mg ca and 18o data suggest it is at 50 m of the three species n dutertrei is the most sensitive to dissolution up to 23 decrease in shell mg ca per km while g sacculifer is the most resistant

thirteen thousand years of southeastern mediterranean climate variability inferred from an integrative planktic foraminiferal based approach over the past 13 ka the hydrology for the southeastern mediterranean was mainly regulated by nile river runoff which in turn was controlled by climate forcing being affected by orbital forcing and the position of the intertropical convergence zone itcz planktic foraminiferal data assemblages stable isotopes and size properties indicate three major periods 1 from 13 0 to 11 5 ka the upper water column was well mixed cold and productive 2 from 11 5 to 6 4 ka hydrology and foraminifers were affected by intensified monsoonal circulation the enhanced size of globigerinoides ruber is interpreted as a response to environmental stress caused by low saline waters 3 after 6 4 ka the southward retreat of the itcz caused a decrease in freshwater discharge and hence a return to ecological equilibrium a drop in foraminifer diversity from 2 9 to 1 1 ka was related to more arid conditions and limited supply of nutrients from the nile river we suggest a link to a negative north atlantic oscillation nao marking the roman humid period in the western mediterranean and in anti phase with the southeastern mediterranean aridity because nile river runoff exerted major control on surface hydrology a connection to indian and pacific climate systems partially controlling precipitation over the nile catchment area is hypothesized from 1 1 to 0 54 ka high foraminifer diversity indicates humid conditions synchronous to the medieval climate anomaly under a positive nao state over the past 0 54 ka encompassing the little ice age another arid period is indicated by a drop in foraminifer diversity

stability of the kuroshio path with respect to glacial sea level lowering 1 we investigate the changes of the kuroshio current in the east china sea during the last glacial maximum based on numerical experiments using an ocean model and geochemical analyses of marine sediments our numerical experimental results indicate that there was little effect of sea level change on the path of the kuroshio during the glacial period geochemical proxy records of marine sediment cores recovered from inside and outside the okinawa trough ot show no significant difference in glacial sea surface temperature and planktonic foraminiferal 18o between the ot and the ryukyu forearc this indicates that the glacial sea surface temperature and salinity were almost the same inside and outside the ot hence during the glacial period kuroshio water most likely intruded into the ot and flowed along the shelf break until it drained out through the tokara strait

scales of transient convective support beneath africa beneath sub equatorial africa there is convincing evidence for a gigantic slow velocity anomaly within the lower mantle that is inferred to be a thermochemical superplume here we define the spatial and temporal pattern of uplift across the northern edge of this putative superplume by analyzing stratal geometries and stacking velocities of neogene sedimentary rocks these marine deposits are imaged on a dense grid of seismic reflection profiles that straddle the southwest african coastal shelf inverse modeling of stacking velocity profiles demonstrates that there have been at least two significant phases of uplift a post pliocene uplift event increases from 0 to 500 m elevation over a distance of 1000 km in close agreement with geophysical estimates of the present day variation of dynamic topography an earlier phase of uplift occurred in middle oligocene time ca 30 35 ma ago we propose a two stage development of epeirogeny in which a middle oligocene phase of uplift may be related to initiation and growth of the african superplume post pliocene denudation records rapid 100 250 m ma vertical motions generated by upper mantle convection which vary on length scales of 500 1000 km our results support the existence of a convective circulation system that has operated on different temporal and spatial scales beneath the african plate

upper mantle sh and p velocity structures and compositional models beneath southern africa abstract we constrain sh and p wave velocity structures in the upper mantle beneath southern africa using triplicated phases recorded in the epicentral distance range of 11 28 for one shallow event we then explore thermal and compositional models appropriate for explaining the inferred seismic structures in the region both sh and p wave data suggest presence of a low velocity zone with velocity reductions of at least 5 for s waves and 2 for p waves beneath a 150 km thick high velocity lithospheric lid seismic observations also suggest that the p s ratio is larger 1 88 in the transition zone than in the lithospheric lid 1 70 the inferred p wave velocity jump across the 660 km discontinuity is small

a comparative evaluation of the parallel flow and spherical reservoir models of hdr geothermal systems abstract a terminology is developed to link two conceptual semi analytical models of hdr geothermal energy extraction through the common criterion of reservoir volume the first is a parallel fracture model pfm that represents thermal recovery from an arrangement of prismatic blocks thermally isolated from the geologic host medium the second is a spherical reservoir model srm that admits energy recovery from both a central production zone and the surrounding geologic body behaviour of the two different but complementary systems are governed by the dimensionless variables of thermal drawdown t d circulation rate q d and time t d with the pfm further conditioned by a diffusion length ratio representative of the fracture spacing thermal response of the pfm exhibits a worst case threshold for thermal recovery at small magnitudes of circulation rate q d corresponding to the system progressing in near thermal equilibrium a close correspondence exists between the thermal response of the pfm for low q d and that of the srm for high q d where the influence of external heat supply is not apparent circulation tests conducted in existing reservoirs return magnitudes of q d and diffusion length ratios that suggest they are operating close to thermal equilibrium as predicted from the pfm with this determined a priori the assumptions made in the srm are not violated suggesting the significant contribution that external heat supply may make to the gross energy recovery as predicted by the srm energy recovery remains practically unbounded for relevant magnitudes of q d with this effect being noticeable well within the projected reservoir lifetime

density structure of the cratonic mantle in southern africa 1 implications for dynamic topography abstract the origin of high topography in southern africa is enigmatic by comparing topography in different cratons we demonstrate that in southern africa both the archean and proterozoic blocks have surface elevation 500 700 m higher than in any other craton worldwide except for the tanzanian craton an unusually high topography may be caused by a low density high depletion of the cratonic lithospheric mantle and or by the dynamic support of the mantle with origin below the depth of isostatic compensation assumed here to be at the lithosphere base we use free board constraints to examine the relative contributions of the both factors to surface topography in the cratons of southern africa our analysis takes advantage of the sase seismic experiment which provided high resolution regional models of the crustal thickness we calculate the model of density structure of the lithospheric mantle in southern africa and show that it has an overall agreement with xenolith based data for lithospheric terranes of different ages density of lithospheric mantle has significant short wavelength variations in all tectonic blocks of southern africa and has typical spt values of ca 3 37 3 41 g cm 3 in the cape fold and namaqua natal fold belts ca 3 34 3 35 g cm 3 in the proterozoic okwa block and the bushveld intrusion complex ca 3 34 3 37 g cm 3 in the limpopo belt and ca 3 32 3 33 g cm 3 in the kaapvaal and southern zimbabwe cratons the results indicate that 0 5 1 0 km of surface topography with the most likely value of ca 0 5 km cannot be explained by the lithosphere structure within the petrologically permitted range of mantle densities and requires the dynamic or static contribution from the sublithospheric mantle given a low amplitude of regional free air gravity anomalies ca 20 mgal on average we propose that mantle residual dynamic topography may be associated with the low density region below the depth of isostatic compensation a possible candidate is the low velocity layer between the lithospheric base and the mantle transition zone where a temperature anomaly of 100 200 c in a ca 100 150 km thick layer may explain the observed reduction in vs velocity and may produce ca 0 5 1 0 km to the regional topographic uplift

laurentide ice sheet meltwater and abrupt climate change during the last glaciation 1 a leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the north american laurentide ice sheet lis which may have routed fresh water between the gulf of mexico gom and the north atlantic affecting north atlantic deep water variability and regional climate paired measurements of 18o and mg ca of foraminiferal calcite from gom sediments reveal five episodes of lis meltwater input from 28 to 45 thousand years ago ka that do not match the millennial scale dansgaard oeschger warmings recorded in greenland ice we suggest that summer melting of the lis may occur during antarctic warming and likely contributed to sea level variability during marine isotope stage 3

variability of the large scale general circulation of the mediterranean sea from observations and modelling a review abstract in this paper we present an overview of the most recent findings about the mediterranean sea present day circulation structure both historical observations and numerical model simulations are presented outlining the differences and agreement the model simulations are presented for both an eddy resolving and a coarse resolution numerical model and the results are intercompared the importance of the mesoscales in modifying the large scale flow field is elucidated the critical point is the discovery of the large amplitude interannual variability of the circulation and water mass structure associated with the anomalies of atmospheric forcing over the basin the seasonal variability can be strictly related to changes in heat and momentum fluxes while the interannual variability has a component which is related to the mesoscale field the latter is very intense in the algerian current region and levantine basin but different in structure in the two regions results are shown which confirm the importance of wind driving in establishing the kinetic energy of the flow field by comparing the current transport at the strait of corsica with observations in conclusion the essential characteristics of the present day circulation are associated with the atmospheric forcing and the basin topographic structure results from palaeoceanographic simulations for the last 20 000 years show that changing the atmospheric forcing can cause large changes in the circulation structure which may have affected sapropel formation

timing and mechanism for intratest mg ca variability in a living planktic foraminifer abstract geochemical observations indicate that planktic foraminifer test mg ca is heterogeneous in many species thereby challenging its use as a paleotemperature proxy for paleoceanographic reconstructions we present mg ca and ba ca data collected by laser ablation icp ms from the shells of orbulina universa cultured in controlled laboratory experiments test calcite was labeled with ba spiked seawater for 12 h day or night calcification periods to quantify the timing of intratest mg banding across multiple diurnal cycles results demonstrate that high mg bands are precipitated during the night whereas low mg bands are precipitated during the day data obtained from specimens growing at 20 c and 25 c show that mg ca ratios in both high and low mg bands increase with temperature and average test mg ca ratios are in excellent agreement with previously published empirical calibrations based on bulk solution icp ms analyses in general mg band concentrations decrease with increasing ph and or co2 3 but this effect decreases as experimental temperatures increase from 20 c to 25 c we suggest that mitochondrial uptake of mg2 from the thin calcifying fluid beneath streaming rhizopodial filaments may provide the primary locus for mg2 removal during test calcification and that diurnal variations in either mitochondrial density or activity produce mg banding these results demonstrate that mg banding is an inherent component of test biomineralization in o universa and show that the mg ca paleothermometer remains a fundamental tool for reconstructing past ocean temperatures from fossil foraminifers

thermochemical structure and dynamics of the african superplume 1 we present a new three dimensional 3 d model of the thermochemical structure of the african superplume region obtained from simultaneous inversion of global seismic and convection related data convection related observations include the global free air gravity field tectonic plate motions dynamic surface topography and the excess ellipticity of the core mantle boundary a 3 d image of the chemically induced density perturbations provides direct evidence that intrinsically dense material is entrained within the superplume and concentrated into a rounded structure 1000 km above the core mantle boundary the thermally induced density perturbations are greater in magnitude than the chemically induced implying overall positive buoyancy throughout the superplume the observed morphology and density signatures are consistent with a thermochemical plume that has risen from a compositionally distinct pile at the base of the mantle and may be currently deforming under the influence of its intrinsic negative chemical buoyancy citation simmons n a a m forte and s p grand 2007 thermochemical structure and dynamics of the african superplume geophys res lett 34 l02301 doi 10 1029 2006gl028009

mantle dynamics isostasy and the support of high terrain dynamic topography is commonly understood to be deflection of the earth s surface that results from convection of the mantle because different authors use the words dynamic topography differently topography designated as dynamic may amount to only a few hundred meters or may exceed 2000 m for most regions however surface heights computed on the assumption that the lithospheric column is in isostatic equilibrium provide good approximations to observed topography the small free air gravity anomalies and still smaller isostatic anomalies 2000 m of dynamic topography moreover simple examples show that if flow induced stresses maintain a given density distribution then the resultant surface deflections can be smaller than those that would exist in isostatic equilibrium in light of confusion over the term dynamic topography we offer readers simple tools that we hope will enable them to diagnose the component of topography that results from flow induced stresses and to distinguish it from topography that is compensated isostatically

mantle anomalies beneath southern africa evidence from seismic s and p receiver functions summary to understand deep structure and processes beneath southern africa we apply the doublestacking version of the s receiver function srf technique to the recordings of the south african seismic experiment in this technique the wavefields of s and sks are separated by space time filtration and the receiver functions are constructed separately for the s and sks seismic phases the results are consistent with those obtained from the srfs of the permanent stations bosa and lbtb evidence for a reduced s velocity atop the 410 km discontinuity is present in both srfs and p receiver functions the s velocity contrast at the 410 km discontinuity is 40 per cent larger than the norm and there are observations of s350p and p350s seismic phases from the negative 350 km discontinuity beneath the kaapvaal craton the s350p and p350s phases display a dependence on the azimuth which can be caused by anisotropy in the layer atop the 350 km discontinuity this dependence is consistent with observations of shear wave splitting in sks there are observations of the s450p phase from the 450 km negative discontinuity in the transition zone the most anomalous transition zone is found close to the region where the kalahari craton was located in the mesozoic lateral variations of the s velocity are found beneath the 660 km discontinuity teleseismic s and p traveltime residuals with respect to iasp91 model are evaluated from the traveltimes of the p410s and pp410s seismic phases in the uppermost mantle these residuals as well as s410p traveltimes require a reduced vp vs ratio around 1 75 0 01 versus 1 8 in iasp91 an effect of the depletion of the mantle lithosphere in basaltic material in the models obtained by a joint inversion of the receiver functions and the teleseismic traveltime residuals the low velocity zone lvz with the onset of low velocity at a depth of 140 20 km is present at most locations the minimum s velocity in the lvz is 4 5 km s 1 the lvz in our models is consistent with the s velocity vp vs velocity ratio and depth range of high temperature lerzholites in the mantle xenoliths from southern africa our most intriguing finding is a very low quality factor qs on the order of a few tens in the upper mantle we interpret high attenuation the lvz and the low s velocity atop the 410 km discontinuity as the effects of plume like phenomena in the upper mantle

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

evolution of the mg ca ratio of cretaceous seawater implications from the composition of biological low mg calcite abstract for the evaluation of variations in the cretaceous seawater mg ca ratio 12 shells of rudist bivalves ranging in age from the late barremian 112 2 ma to the early campanian 81 4 ma have been analysed for intra shell variations in chemical mg sr fe mn and isotopic 18 o 13 c compositions of low mg calcite preservation of fibrous prismatic ultrastructure low fe and mn concentrations as well as sr concentrations within the range of marine biological calcite indicate only very minor diagenetic alteration in all studied shells mg concentrations and 18 o values show a more or less well defined inverse covariance this pattern is similar to the conditions observed in modern skeletal calcite and interpreted to result from a combination of a temperature effect and an unidentified metabolic control on the incorporation of mg into calcite average mg concentrations in rudist calcite are significantly lower than those of modern bivalves and increase from the barremian albian to the campanian while slopes of 18 o mg regressions are similar to those of modern bivalves assuming that the mg incorporation is linearly dependent on the mg ca ratio of seawater and that mg incorporation into calcite of modern bivalve mollusks follows the same metabolic pathway than in their extinct cretaceous relatives the mg ca molar ratio of cretaceous seawater increased from 1 in the late barremian to 3 in the early campanian this trend matches previous model predictions of seawater composition and experimental results from fluid inclusions in halite a very low mg ca ratio of seawater is confirmed here to have occurred before the onset of the significant mid cretaceous increase of seafloor production rates in the late barremian uncertainties in the secular variations of seafloor spreading are discussed as hydrothermal alteration of young oceanic crust is an important driver of changes in the seawater mg ca ratio

sediment trap and deep sea coretop sediments as tracers of recent changes in planktonic foraminifera assemblages in the southeastern ultra oligotrophic levantine basin abstract sediment trap and core top sediments were used to study the seasonal and longer term variability in the distribution and assemblage composition of planktonic foraminifera pf in the ultra oligotrophic eastern mediterranean levantine basin lb a continuous time series of particulate flux sampled every 11 12 days were retrieved from a sediment trap deployed at 1300 m between may 2017 and may 2018 the core top sediments were collected close to the sediment trap mooring site at 1500 m water depth the average annual planktonic foraminiferal pf flux was 93 shells m 2 d 1 the lowest value yet recorded among traps located in tropical subtropical oligotrophic regions a bimodal increase in pf flux is observed with highest numbers of 452 shells m 2 d 1 occurring in winter february responding directly to maxima in particulate mass flux a lower flux occurs in late summer from mid august to mid september with up to 197 shells m 2 d 1 ten species were found in the trap the majority were symbiont bearing spinose species that contribute 96 of the total flux globigerinoides ruber white predominate the assemblage composition during the winter peak together with globoturborotalita rubsecens and globigerinella calida during the subordinate summer peak the dominating species were g ruber white orbulina universa and globigerinoides ruber pink the relative abundance of g bulloides and g ruber pink is much lower in the sediment trap samples compared to their abundance in nearby coretop sediments this trend seems to indicate a recent drop in their numbers at the same time g rubescens and globoturborotalita tenella occur in higher numbers in the sediment trap compared with the coretop samples these opposite trends may reflect the current adjustment of certain pf species to the ongoing sea surface warming and decrease in food availability in the lb

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

neoproterozoic to early cambrian crustal evolution of the pan african saldania belt south africa abstract the saldania belt forms part of a system of neoproterozoic mobile belts that surround and weld older cratons on the african continent it is a poorly exposed low grade orogenic belt composed of a number of inliers unroofed in mega anticlinal hinges of the permo triassic cape fold belt along the southern tip of africa deformed meta volcanosedimentary units are contained within tectonostratigraphic terranes separated by deep rooted sinistral dextral strike slip fault zones which display evidence of prolonged reactivation sedimentary rocks and volcanics of the boland terrane malmesbury group lower kango group and gamtoos group are considered to be distal facies of rift successions overlying the mid proterozoic crystalline basement on the southwestern edge of the kalahari craton these lithologies have been deposited in semi pull apart basins that formed in response to the breakup of rodinia and progressive opening of the proto atlantic adamaster ocean from 780 750 ma fragments of juvenile pan african crust with wpb morb characteristics occur in the bridgetown formation swartland terrane malmesbury inlier and attest to ocean floor spreading in this belt the thick turbidite successions of the swartland and tygerberg terranes malmesbury group reflect deeper water conditions and were deposited partly on oceanic crust in an evolving ocean continental margin basin marked by increasing sea levels and reduction of continental freeboard reversal of spreading and closing of the adamastor ocean possibly initiated by the opening of iapetus occurred in the period 600 570 ma although this movement vector caused sinistral transpressional reactivation of the gariep and saldanian margins there is no proper collision orogen developed in the saldania belt the bridgetown formation represents the suture between the southern rifted margin succession of the kalahari craton and a poorly developed southern orogenic belt represented in part by the swartland and tygerberg terranes this geosuture is similar to that of the south atlantic which formed in the analogous gariep belt between 575 and 543 ma multiphase s i and a type granites of the cape granite suite intruded the saldania belt in a pervasive transpressive regime between 550 and 510 ma comparing well with the timing of peak metamorphism collision in the gariep belt 545 ma the absence of a proper collisional orogen and the strongly developed northwesterly structural grain in the saldania belt seem to suggest that the cape granite suite was generated in a strike slip regime a discrepancy of approximately 50 ma between the age of the collision granites of the dom feliciano belt and cape granite suite suggests that they are genetically unrelated similarities in structural styles magmatism and dated events between the saldania ross delamarian chain of orogens however indicate a common history the evolution of this chain and that of the gariep damara dom feliciano belts can be accommodated in a single plate tectonic model of simultaneous sinistral transpressive subduction driven by the rifting of laurentia from south america and opening of the iapetus ocean loading and depression of the western and southern kalahari craton margin by thrust stacks of the late neoproterozoic orogens led to the formation of syn to post orogenic peripheral foreland basins such as those represented by the nama and vanrhynsdorp groups lowering of sea level and increased continental freeboard deposition of the unconformity based upper kango group and possibly the molassic franschhoek formation occurred in intra orogen pull apart basins which possibly developed between 530 and 510 ma in the saldania belt

benthic foraminiferal mg ca paleothermometry a revised core top calibration core top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium calcium mg ca to bottom water temperatures bwt benthic foraminifera collected from hawaii little bahama bank sea of okhotsk gulf of california ne atlantic ceara rise sierra leone rise the ontong java plateau and the southern ocean covering a temperature range of 0 8 to 18 c were used to revise the cibicidoides mg ca temperature calibration the mg ca bwt relationship of three common cibicidoides species is described by an exponential equation mg ca 0 867 0 049 exp 0 109 0 007 bwt stated errors are 95 ci the temperature sensitivity is very similar to a previously published calibration however the revised calibration has a significantly different preexponential constant resulting in different predicted absolute temperatures we attribute this difference in the preexponential constant to an analytical issue of accuracy some genera notably uvigerina show apparently lower temperature sensitivity than others suggesting that the use of constant offsets to account for vital effects in mg ca may not be appropriate downcore mg ca reproducibility as determined on replicate foraminiferal samples is typically better than 0 1 mmol mol 1 2 s e thus considering the errors associated with the cibicidoides calibration and the downcore reproducibility bwt may be estimated to within 1 c application of the revised core top mg ca bwt data to cenozoic foraminiferal mg ca suggests that seawater mg ca was not more than 35 lower than today in the ice free ocean at 50 ma

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

formation of an archaean continent about 30 of the earth is covered by continents but only about 10 small kernels of these continentsae known as archaean cratonsae are continental fragments formed before 2 5 gyr ago the kaapvaal craton of south africa which formed and stabilized between 3 7 and 2 7 gyr ago is one of the oldest reasonably sized examples of these continental fragments it consists of a mosaic of subdomains that have been welded together by processes similar to those of modern day plate tectonics the earliest subdomains may have owed their origin to the onset of efficient recycling from the earth s hydrosphere into the mantle

layered mantle at the karelian craton margin p t of mantle xenocrysts and xenoliths from the kaavi kuopio kimberlites finland peridotitic clinopyroxene cpx and pyrope garnet xenocrysts from four kimberlite pipes in the kaavi kuopio area of eastern finland have been studied using major and trace element geochemistry to obtain information on the vertical compositional variability of the underlying mantle the xenocryst data when combined with the petrological constraints provided by peridotite xenoliths yield a relatively complete section through the lithospheric mantle single grain cpx thermobarometry fits with a 36 mw m2 geotherm calculated using heat flow constraints and xenolith modes and geophysical properties ni thermometry on pyrope xenocrysts gives 700 1350 c and based on the cpx xenocryst xenolith geotherm indicates a wide sampling interval ca 80 230 km plotting pyrope major and trace element compositions as a function of temperature shows there are three distinct layers in the local lithospheric mantle 1 a low temperature 850 c harzburgite layer distinguished by ca rich but ti y and zr depleted pyropes the xenoliths originating from this layer are all fine grained garnet spinel harzburgites with secondary cpx 2 a variably depleted lherzolitic harzburgitic and wehrlitic horizon from 950 to 1150 c or 130 to 180 km 3 a deep layer from 180 to 240 km composed largely of fertile material the peridotitic diamond window at kaavi kuopio stretches from the top of the diamond stability field at 140 km to the base of the harzburgite bearing mantle at about 180 km implying a roughly 40 km wide prospective zone

microplankton response to environmental conditions in the alboran sea western mediterranean one year sediment trap record abstract the present work analyses the seasonal evolution of planktonic assemblages and particle fluxes through the water column in the eastern alboran sea western mediterranean at 35o55 47 n 01o30 77 w a sediment trap was deployed below the influence of the almeria oran front aof a semi permanent geostrophic front during july 1997 to june 1998 overall the temporal variability of coccolithophore planktonic foraminifer diatom benthic and wind carried biogenic particle fluxes is linked to the seasonal evolution of sea surface hydrological structures maximum planktonic fluxes were found during high productivity periods and wind induced upwelling following a trimodal pattern with maximum fluxes in july 1997 november december 1997 and april may 1998 these periods were characterized by vertical mixing and the full development of anticyclonic gyres in the alboran sea the annual flux of coccolithophores was dominated by the small gephyrocapsa group and emiliania huxleyi whereas turborotalita quinqueloba and globigerina bulloides dominated the foraminiferal fluxes and chaetoceros resting spores rs were predominant in the diatom assemblage benthic specimens were also collected with the sediment trap suggesting a variable influence of bottom water activity wind driven particles phytoliths and fresh water diatoms were collected along the year but their fluxes followed the local wind regime the high sea surface temperature sst during fall due to weaker than usual westerly winds and the pressure anomaly prevailing in the alboran sea during early winter were reflected in the planktonic assemblages by the proliferation of warm lower photic layer inhabitants and or oligotrophic taxa of coccolithophores florisphaera profunda planktonic foraminifers globigerinoides ruber and globorotalia inflata and diatoms leptocylindrus danicus these unusual climatic conditions in the eastern alboran sea must have been caused by the 1997 1998 enso event

boron calcium ratios in globigerinoides ruber from the arabian sea implications for controls on boron incorporation abstract culture and downcore studies have been used to argue that b ca ratios in planktic foraminifera are correlated with seawater ph and may record seawater borate bicarbonate ratios although other factors may also control b ca specimens of globigerinoides ruber from the ocean drilling program odp site 723a western arabian sea and core aas9 21 eastern arabian sea from the last 22 kyr were analysed for b ca 18 o and mg ca b ca was compared to reconstructed salinity and sea surface temperature sst records to gain insight into the processes controlling the incorporation of boron in both cores b ca and mg ca are positively correlated which suggests that temperature governs the incorporation of boron in g ruber to some extent higher b ca ratios at the site affected by upwelling odp 723a than in the non upwelling region core aas9 21 and a positive correlation between b ca and shell size in g ruber are observed we observe no significant correlation between b ca in g ruber and salinity ph or dissolved inorganic carbon dic in either the western or eastern arabian sea which throws considerable doubt on the utility of b ca ratios as a ph or pco 2 proxy

theory of thermal recovery from a spherically stimulated hot dry rock reservoir a conceptual model is presented to describe thermal recovery from a semi infinite hot dry rock hdr geothermal reservoir containing an equidimensional permeable zone transient behavior may be represented uniquely by five dimensionless parameters variation in production temperature td with time td is influenced by reservoir throughput qd thermal porosity d and depth ratio a z of these only throughput qd exercises significant control on transient performance the parameter being directly proportional to reservoir circulation rate and inversely proportional to the effective radius of the stimulated zone steady production temperature td is indexed to throughput qd and depth ratio a z only steady production temperatures are always highest for a host medium bounded by a proximal constant temperature surface and lowest for an insulated boundary boundary effects are insignificant for reservoir burial depths up to an order of magnitude greater than the reservoir radius a threshold behavior in time tdqd is evident for very large reservoir throughput qd this bounding behavior describes in dimensionless time the maximum rate at which thermal depletion may occur this state is evident for large dimensionless throughput magnitudes qd corresponding directly with high circulation rates within the reservoir predictions compare favorably with results from a 300 day circulation test at the fenton hill geothermal energy site new mexico

planktonic foraminifers as tracers of ocean currents in the eastern south atlantic the standing stock of planktonic foraminifers collected at 16 stations by multinet plankton tow has been examined in five discrete depth intervals 0 25 m 25 50 m 50 100 m 100 150 m and 150 300 m the assemblages document the status of populations in the surface and subsurface waters of the southeast atlantic during february march 1988 standing crops document hydrographic conditions in the coastal and geostrophic branch of the benguela current the angola current the tropical cyclonic gyre and the south equatorial current standing stocks are highest when primary production is intermediate very high primary production reduces foraminiferal crops significantly eleven species occur abundantly average 10 of the total standing stock a few species g glutinata g quinqueloba g clarkei are abundant at each station whereas the occurrence of other species g ruber g sacculifer g scitula g menardii g crassaformis n incompta n dutertrei is spatially restricted g ruber g rubescens and g glutinata are abundant in high salinity surface water also g ruber is abundant within the equatorial undercurrent water when this water is brought to the surface high concentrations of n incompta and g bulloides are observed in the angola benguela front when nutrient concentration is moderately elevated in surface and subsurface water upper part of the thermocline g crassaformis becomes abundant in the subsurface water of the angola benguela front this species is restricted to lower oxygenated subsurface water and traces incursions of water transported by the angola current g menardii is considered as an indicator for the equatorial undercurrent below the mixed layer whereas g scitula most probably points to an admixture of water transported by the northward flowing benguela current high abundances of g quinqueloba g clarkei in the surface and subsurface waters reflect favorable nutrient conditions like those present in the geostrophic benguela current and in the equatorial divergence zone g falconensis n dutertrei and g siphonifera appear to trace the southern equatorial current

dispersed fluid flow in fractured reservoirs an analysis of tracer determined residence time distributions a methodology for analyzing the internal flow characteristics of a fractured geothermal reservoir using tracer determined residence time distribution curves is outlined emphasis is placed on comparison of the statistical quantities obtained from the tracer curves of different reservoirs or of the same reservoir under different conditions in this way model independent information may be used unambiguously to construct empirical reservoir performance correlations downhole measurements of the tracer response exiting from discrete fracture zones permit further characterization of reservoir fluid flow behavior tracer experiments conducted in prototype hot dry rock geothermal reservoirs in fractured rock are examined using these statistically based data analysis methods

li sr mg and na in foraminiferal calcite shells from laboratory culture sediment traps and sediment cores abstract constant temperature laboratory culture experiments of the planktonic foraminiferal species globigerinoides sacculifer brady suggest that the ratios of li and sr to ca in the shells are a function of these ratios in the culture solutions mg ca and na ca in the shells did not vary with changes of these ratios in the culture solution these are the first direct determinations of the relationship between foraminiferal shell chemistry and solution composition the possibility of temperature dependence for the minor elemental composition of foraminiferal shells was also investigated in the laboratory and by analysis of several planktonic and one benthic foraminiferal species from sediment trap and sediment core samples the sr ca mg ca and na ca ratios in the natural samples roughly correlate with calcification temperature whereas differences in the li ca ratios are small and not systematically related to temperature however laboratory culture experiments at 20 c and 30 c showed no variation in the li ca sr ca mg ca and na ca ratios with calcification temperature for the planktonic foraminifera g sacculifer and orbulina universa therefore observed differences in the sr ca mg ca and na ca ratios for the sediment trap and core foraminiferal samples cannot be ascribed to direct effects of calcification temperature but may be due to some other environmental factor which is correlated with temperature

temperature control on the incorporation of magnesium strontium fluorine and cadmium into benthic foraminiferal shells from little bahama bank prospects for thermocline paleoceanography surface sediments from little bahama bank lbb intersecting the subtropical thermocline were used to assess the influence of temperature on the incorporation of mg sr f and cd into shells of benthic foraminifera samples were obtained from twelve cores along the southern slope of lbb covering a temperature range of 18 4 5 c between 301 and 1585 m we studied the composition of ten calcitic and one aragonitic species which are often used in paleochemical reconstructions mg ca ratios decrease with increasing water depth in all benthic species both with calcitic and aragonitic mineralogy showing a strong correlation with water temperature similar decrease is seen in sr ca but with no correlation with temperature none of the benthic species studied here exhibits a depth or temperature related change in f ca similar trends are observed when using an ocean wide dataset which includes shallow and deep core tops 300 5000 m we suggest that temperature is the primary control on the mg content of benthic foraminifera based on inorganic precipitation experiments and thermodynamic considerations presented here a 30 40 decrease in the mg distribution coefficient in calcite may be expected as a result of a temperature change from 25 c to 5 c which is about half the observed change in lbb a calibration curve applied to c pachyderma data from core tops along the slope of little bahama bank suggests that water temperature may be inferred from mg ca ratios with an uncertainty of about 0 8 c therefore the mg content of benthic foraminifera may provide a new independent temperature proxy for studying shallow waters paleoceanography the linear decrease in sr ca with increasing depth is not correlated with temperature the trend is constant from the ocean surface down to 5 km suggesting that pressure related effects on the calcification process are a more likely explanation than post depositional dissolution mg ca ratios in aragonitic shells of h elegans covary with temperature in accord with recent observations from corals in contrast the sr and f chemistry of h elegans is very different than that of corals and inorganically precipitated aragonites the disparities between the elemental composition of biogenic and inorganic phases and the large intergeneric and interspecific differences observed both in planktonic and benthic foraminifera implicate temperature related physiological processes in regulating the coprecipitation of elements in foraminiferal shells our work demonstrates that cd ca ratios of shallow calcitic species reflect the vertical distribution of nutrients no significant influence of temperature on the partitioning of cd into the shells was found our data extend the previous deep water calibration boyle 1992 thereby allowing for the reconstruction of the nutrient chemistry of shallow thermocline waters

regional and interannual productivity of biogenic components and planktonic foraminiferal fluxes in the northwestern pacific basin abstract time series sediment trap experiments at subtropical wct 1 and subarctic wct 2 stations in the northwestern pacific indicate seasonal latitudinal and depth variations in total particulate biogenic and foraminiferal fluxes at the subtropical station the average total mass flux was 19 4 mg m 2 day 1 in the shallow trap 1060 m and 21 5 26 1 mg m 2 day 1 in the deep trap 3930 m during the sampling period at subarctic station these values were 91 5 176 9 mg m 2 day 1 in the shallow and 68 6 112 3 mg m 2 day 1 in the deep trap we recognized 12 and 15 planktonic foraminiferal species at station wct 1 and station wct 2 respectively the planktonic foraminiferal flux and species turnover are related to seasonal and interannual changes in source water and water column conditions at both stations at station wct 1 the highest flux was recorded during the summer with a peak in mid to late june associated with similar flux patterns of the dominant species globigerinoides ruber and globigerinita glutinata the total flux of foraminiferal tests at the shallow and deep traps is similar in numbers and magnitude at station wct 2 the peaks of total flux of foraminiferal tests at the two trap depths differ in number and their magnitude in the deep trap is almost half of that in the shallow trap a distinctive seasonal pattern occurred in the shallow and the deep trap with a peak in total foraminiferal flux in mid june to mid july globigerina quinqueloba neogloboquadrina pachyderma and neogloboquadrina dutertrei dominate the planktonic population throughout the year subtropical station wct 1 was characterized by low total foraminiferal fluxes and low total mass flux which is dominated by calcium carbonate and depleted in opal whereas high foraminiferal fluxes and a high total mass flux dominated by high biogenic opal and less calcium carbonate and organic matter characterize subarctic station wct 2 the foraminiferal carbonate that reaches the seafloor accounts for an average 20 27 and 22 23 of the total calcium carbonate at station wct 1 and station wct 2 respectively the primary reason for the difference in flux at both stations thus lies in the different contributions of siliceous and calcareous planktonic assemblages the seasonal variation in biogenic particulate flux at both stations implies that temporal changes in biological productivity are governed by large scale seasonal climatic variability and local hydrography

anomalous bathymetry and palaeobathymetric models of the mozambique basin and riiser larsen sea abstract in this study we introduce a palaeobathymetric model for the conjugate mozambique basin and riiser larsen sea built by employing backstripping techniques compensating for dynamic topography and plate motions the model is presented at 0 2 0 2 grid resolution making it suitable for future oceanographic and climate simulation model experiments aimed at a better understanding of the climatic and oceanographic relevance of oceanic gateways in the southern ocean at the present day the seafloor next to the mozambican continental margin is around 300 m shallower and that in the central mozambique channel is almost 1300 m shallower than their conjugate areas or the predictions of oceanic thermal subsidence models the cause of this anomalous depth is difficult to determine confidently because of sparse data in particular concerning sediment thickness and because of the wide range of amplitudes in modelled present day dynamic topography the distribution of shallow seafloor suggests that it might be attributed to the presence of thicker than usual oceanic crust which in turn can be attributed to the paleogene passage of the quathlamba plume beneath the basin we portray these effects in our palaeobathymetric models in contrast the riiser larsen sea has experienced fairly stable subsidence since its formation in jurassic times with only slight observable changes attributable to the onset of antarctic glaciation and during the middle miocene climate transition both basins display flexure over half wavelengths of 60 80 km with amplitudes of 1500 m towards their continental margins this plays an important role in models of palaeobathymetry for times older than 100 ma near the margins isolated areas of transitional or debatable crustal composition including beira high and gunnerus ridge are depicted to subside in a similar fashion to oceanic crust further into the indian ocean oceanic lithosphere younger than 100 ma on both plates has subsided to depths that are typical of thermal subsidence models finally the new palaeobathymetry had distinct consequences for the current systems in the young southern ocean during the time periods the onset of coast parallel bottom currents and associated contourite deposition in the mozambique channel at palaeo water depths of 3500 4000 m may be a consequence of either an opening of a deep water passage into the south atlantic between southwest indian ridge and agulhas plateau or into the tethys ocean in the late cretaceous

imprints of high salinity water plumes originating from the red sea during termination ii abstract the investigation of a core collected in the socotran area western indian ocean provides new insights into water mass exchanges between the red sea and the gulf of aden through the strait of bab el mandeb during the penultimate deglaciation the benthic oxygen isotope record documents the occurrence of stillstands and possibly reversals within the general trend of sea level rise plumes of warm and salty waters are recorded at the surface of the arabian sea and as far as the socotran coast for each increase in sea level these plumes disappeared whenever global sea level stopped rising or showed a brief lowering according to their high salinities these plumes can only originate in the red sea the sill of bab el mandeb becoming deeper and wider during the deglaciation allowed greater exchange between both seas and stronger flow out of the red sea at each episode of sea level rise isotopic and faunal evidence suggest a strengthening of coastal upwelling in the arabian sea during these periods this increase in upwelling activity may explain how plumes of highly saline waters were maintained at the surface moreover the high salinity surface plumes may have facilitated upwelling activity through the destabilisation of density stratification in the upper water column the occurrence of at least high salinity salty water outflows during termination ii confirms the step wise non linear structure of the penultimate deglaciation providing a perfect example of the threshold concept in rapid climate changes

glacial interglacial changes in subantarctic sea surface temperature and δ18o water using foraminiferal mg laboratory culturing experiments with living globigerina bulloides indicate that mg ca is primarily a function of seawater temperature and suggest that mg ca of fossil specimens is an effective paleotemperature proxy using culturing results and a core top neogloboquadrina pachyderma calibration we have estimated glacial interglacial changes in sea surface temperature sst using planktonic mg ca records from core rc11 120 in the subantarctic indian ocean 43 s 80 e and core e11 2 in the subantarctic pacific ocean 56 s 115 w our results suggest that glacial sst was about 4 c cooler in the subantarctic indian ocean and 2 5 c cooler in the subantarctic pacific comparison of sst and planktonic 18o records indicates that changes in sst lead changes in 18o by on average 1 3 kyr the glacial interglacial temperature change indicated by the subantarctic mg ca records suggests that temperature accounts for 40 60 of the foraminiferal 18o change we have used the mg ca based sst estimates and 18o determinations to generate site specific seawater 18o records which suggest that seawater 18o was on average 1 more positive during glacial episodes compared with interglacial episodes

the relationship between shell size and mg ca sr ca δ18o and δ13c of species of planktonic foraminifera the relationship between shell size and mg ca sr ca 18o and 13c of planktonic foraminiferal calcite has been investigated using seventeen species in six different size fractions mg ca increases and sr ca decreases with increasing size except for two globorotaliid species which show the opposite trend the changes in mg ca broadly follow 18o calcification temperatures except that surface and near surface dwelling species show larger changes in mg ca than can be accounted for by differences in calcification temperature derived from 18o the increases in mg ca and decreases in sr ca vary linearly with the well established increase in 13c with size this is consistent with smaller individuals calcifying faster than larger individuals and larger individuals forming calcite that more closely reflects seawater temperature and composition it appears that variations in calcification rate affect mg and sr shell chemistry the observations may account for part of the temporal variability in foraminiferal sr ca within a single size fraction that has been attributed to changes in seawater sr ca

deglaciation in the tropical indian ocean driven by interplay between the regional monsoon and global teleconnections abstract high resolution climate records of the ice age terminations from monsoon dominated regions reveal the interplay of regional and global driving forces speleothem records from chinese caves indicate that glacial terminations were interrupted by prominent weak monsoon intervals wmi lasting a few thousand years deglacial wmis are interpreted as the result of cold temperature anomalies generated by sea ice feedbacks in the north atlantic most prominently during heinrich events recent modeling results suggest however that wmis reflect changes in the intensity of the indian rather than the east asian monsoon here we use foraminiferal trace element mg ca and ba ca and stable isotope records from a sediment core off the malabar coast in the southeastern arabian sea with centennial scale resolution to test this hypothesis and to constrain the nature and timing of deglacial climate change in the tropical indian ocean the malabar deglacial sst record is unique in character and different from other tropical climate records sst at the last glacial maximum was 2 7 0 5 c colder than pre industrial sst deglacial warming started at 18 6 95 ci range 18 8 18 1 kyr bp within error of the onset of warming at other tropical sites as well as in antarctica and the southern ocean and either coeval with or up to 1 kyr before the atmospheric co 2 rise warming took place in two steps separated by an interval of stable sst between 15 7 16 2 14 9 and 13 2 13 9 12 0 kyr bp the 18 o water record and the ba ca record which is a measure of indian sub continent riverine runoff indicate that the last ice age termination was marked by a prominent weak indian monsoon interval interrupted by an intense monsoon phase as seen in speleothem records and predicted by modeling a strong correspondence between the timing of the malabar 18 o sw record and the hulu cave monsoon record suggests that deglacial 18 o changes in both localities dominantly reflect compositional changes in precipitation likely driven by changes in the north atlantic

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