seismic imaging of reservoir flow properties time lapse amplitude changes asymptotic methods provide an efficient means by which to infer reservoir flow properties such as permeability from time lapse seismic data a trajectory based methodology much like ray based methods for medical and seismic imaging is the basis for an iterative inversion of time lapse amplitude changes in this approach a single reservoir simulation is required for each iteration of the algorithm a comparison between purely numerical and the trajectory based sensitivities demonstrates their accuracy an application to a set of synthetic amplitude changes indicates that they can recover large scale reservoir permeability variations from time lapse data in an application of actual time lapse amplitude changes from the bay marchand field in the gulf of mexico we are able to reduce the misfit by 81 in twelve iterations the time lapse observations indicate lower permeabilities are required in the central portion of the reservoir

millennial scale changes in north atlantic circulation since the last glaciation ocean circulation is closely linked to climate change on glacial interglacial and shorter timescales extensive reorganizations in the circulation of deep and intermediate depth waters in the atlantic ocean have been hypothesized for both the last glaciation1 2 3 4 5 6 and the subsequent younger dryas cold interval3 6 7 8 9 10 but there has been little palaeoceanographic study of the subtropical gyres11 12 13 these gyres are the dominant oceanic features of wind driven circulation and as such they reflect changes in climate and are a significant control on nutrient cycling and possibly atmospheric co2 concentrations here we present cd ca ratios in the shells of benthic foraminifera from the bahama banks that confirm previous suggestions11 12 that nutrient concentrations in the north atlantic subtropical gyre were much lower during the last glacial maximum than they are today up to 50 lower according to our data these contrasting nutrient burdens imply much shorter residence times for waters within the thermocline of the last glacial maximum below the glacial thermocline nutrient concentrations were reduced owing to the presence of glacial north atlantic intermediate water a high resolution cd ca record from an intermediate depth indicates decreased nutrient concentrations during the younger dryas interval as well mirroring opposite changes at a nearby deep site3 9 together these observations suggest that the formation of deep and intermediate waters north atlantic deep water and glacial north atlantic intermediate water respectively wax and wane alternately on both orbital and millennial timescales

antarctic ozone depletion causes an intensification of the southern ocean super gyre circulation 1 recent climate trends over the southern hemisphere sh summer feature a strengthening of the circumpolar westerly and a weakening of the midlatitude westerly extending from the stratosphere to earth s surface much of the change is attributable to antarctic ozone depletion however the consequential ocean circulation changes are unknown here i demonstrate that the observed surface wind changes have forced a southward shift and spin up of the super gyre which links the subtropical south pacific indian and atlantic ocean circulation advecting more warm water southward the circulation change includes a strengthening of the east australian current eac flow passing through the tasman sea the southward shift may be responsible for the observed unusually large warming in the sh midlatitude ocean and may contribute to the reported range extension to the south of many marine species in the south west pacific

comment on the oldest south american cricetidae rodentia and mustelidae carnivora late miocene faunal turnover in central argentina and the great american biotic interchange by d h verzi and c i montalvo palaeogeography palaeoclimatology palaeoecology 267 2008 284 291 abstract in a recent paper verzi d h montalvo c i 2008 the oldest south american cricetidae rodentia and mustelidae carnivora late miocene faunal turnover in central argentina and the great american biotic interchange palaeogeography palaeoclimatology palaeoecology 267 284 291 the potentially oldest south american cricetidae rodentia and mustelidae carnivora have been reported from a late miocene huayquerian assemblage located in central argentina caleufu site la pampa province these findings expand the biochron of these important families in south america 3 4 ma earlier than previous records however several observations prevent us from accepting the validity of these assumptions in this paper we discuss the age of the caleufu assemblage and the assignment of the ghunlpam 21722 to mustelidae the caleufu assemblage contains a mixture of pliocene and late miocene faunal elements and has been assigned to the huayquerian only due to the stage of evolution of some rodents the lack of isotopic or paleomagnetic data coupled with the isolation of this locality and the absence of a local stratigraphic succession inhibit its correlation with other palaeontological comparable sites and a robust inference about its chronology the stage of evolution of a taxon is not a biostratigraphic tool thus we cannot rule out the possibility that the caleufu assemblage has an early pliocene montehermosan age the ghunlpam 21722 a poorly preserved specimen shows several characters e g 4 lower incisors mental foramina below the incisors absent third lower incisor smaller than the first and second ones that do not match with mustelidae or carnivora but instead strongly resemble those observed in didelphimorphian marsupials the discussed caveats regarding caleufu assemblage chronology and taxonomy indicate that new and detailed studies are needed before the hypotheses advanced by verzi and montalvo can be accepted

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

delayed holocene reappearance of g menardii the planktonic foraminifera globorotalia menardii absent in the atlantic ocean during the last glacial period reappeared during the holocene as it was present in the indian ocean during glacial time its reappearance might be thought to have been connected to rejuvenation of conveyor circulation but as first shown by glenn jones and confirmed here it was a significant contributor to the atlantic s foraminifer population only after 7000 years ago

plankton biochronology for the last 772 000 years from the western south atlantic ocean abstract calcareous microfossils have potential in the biostratigraphy of pleistocene sediments and a clear relationship with paleoceanographic studies conversely there are few quantitative biostratigraphic studies of chronologically tuned events or sections in the western south atlantic in order to improve the stratigraphical framework for south atlantic paleoceanographic studies the present work attempts to review the last 772 000 years by carrying out a quantitative analysis of the calcareous nannofossil and planktonic foraminiferal assemblages by comparing them with a high resolution marine isotopic record 18 o this work is based on the analysis of two piston cores obtained from the continental slope of the santos basin in the santos drift southeastern brazilian continental margin twelve pleistocene calcareous nannofossil events and twenty planktonic foraminifera events calibrated with oxygen isotopes and correlated with literature stratigraphies are discussed this is the first calcareous plankton biochronology study for the last 772 kyr in the western south atlantic ocean more studies in this region will help to establish a more precise biochronology for these calcareous microfossils this study also presents six new biostratigraphic events of isotopically caibrated planktonic foraminifera which can be used as markers in the western south atlantic

detrital zircon u pb geochronology constrains the age of brazilian neogene deposits from western amazonia abstract the fossiliferous beds of the solimoes formation western brazilian amazon have yielded several vertebrate fossils that are key to understand the evolution of neotropical biotas although this sedimentary unit has been studied for more than two centuries no absolute dates are available so far preventing more precise bio chronostratigraphic interpretations and broader comprehension of the biotic geological events that affected this northern portion of south america during the neogene here we present the first neogene radioisotopic dates for the brazilian amazon via u pb dating of detrital zircon from two classical sites both samples have small proportions of relatively young zircon grains the dates from which are the maximum ages of deposition la icpms analysis of two grains from the niteroi locality yielded a weighted mean of 8 5 0 5 ma and ca tims analysis of two grains from the talisma locality yielded a weighted mean of 10 89 0 13 ma these maximum deposition ages are in the tortonian stage late miocene confirming the age previously inferred based on biochronological data

paired benthic foraminiferal cd ca and zn ca evidence for a greatly increased presence of southern ocean water in the glacial north atlantic benthic foraminiferal 13c and cd ca studies suggest that deep atlantic circulation during the last glacial maximum was very different from today with high nutrient low 13c high cd deep southern ocean water sow penetrating far into the north atlantic however if some glacial 13c values are biased by productivity artifacts and or air sea exchange processes then the existing 13c data may be consistent with the continual dominance of north atlantic deep water nadw cibicidoides wuellerstorfi cd ca results presented here indicate that the glacial north atlantic was strongly enriched in dissolved cd below 2500 m depth if nadw formation was still vigorous relative to sow formation these data could be explained by either increased preformed nutrient levels in the high latitude north atlantic or by increased organic matter remineralization within lower nadw high glacial zn ca values in the same samples however are best explained by a substantially increased mixing with zn rich sow the cause was most likely a partial replacement of nadw by less dense glacial north atlantic intermediate water this reorganization also lowered deep north atlantic co32 concentrations by perhaps 10 to 15 mol kg 1

evidence from the florida straits for younger dryas ocean circulation changes 1 the waters passing through the florida straits today reflect both the western portion of the wind driven subtropical gyre and the northward flow of the upper waters which cross the equator compensating north atlantic deep water export as part of the large scale atlantic meridional overturning circulation it has been postulated from various lines of evidence that the overturning circulation was weaker during the younger dryas cold event of the last deglaciation we show here that the contrast in the oxygen isotopic composition of benthic foraminiferal tests across the florida current is reduced during the younger dryas this most likely reflects a decrease in the density gradient across the channel and a decrease in the vertical shear of the florida current this reduced shear is consistent with the postulated reduction in the atlantic meridional overturning circulation we find that the onset of this change in density structure and flow at the start of the younger dryas is very abrupt occurring in less than 70 years

holocene oscillations of southwest atlantic shelf circulation based on planktonic foraminifera from an upwelling system off cabo frio southeastern brazil the brazil current bc is a relevant feature in the atlantic meridional overturning circulation amoc its behavior during slowdown or intense amoc remains poorly known because of the lack of pal

antarctic sea ice and the control of pleistocene climate instability a hypothesis is presented for the origin of pleistocene climate instability based on expansion of antarctic sea ice and associated changes in the oceans salinity structure the hypothesis assumes that thermohaline overturning is dominated by the reconfigured conveyor of toggweiler and samuels 1993b in which deepwater upwelling is restricted to high southern latitudes the reconfigured conveyor is shown to be potentially stabilized in an on mode by precipitation at high southern latitudes and potentially destabilized into on and off modes by the counteracting influence of antarctic sea ice the mechanism is clarified by the use of a hydraulic analogue we hypothesize that this mechanism accounts for dominant patterns of thermohaline overturning and climate instability between pleistocene warm and cold periods the hypothesis is shown to be consistent with a range of paleoceanographic evidence and to potentially account for details of observed rapid climate changes during glacial and interglacial periods including aspects of interhemispheric timing

seismic detection limits of small deep man made reflectors a test at a geothermal site in northern germany a key question for the development of geothermal plants is the seismic detection and monitoring of fluid injections at several kilometers depth the detection and monitoring limits are controlled by several parameters for example the strength of seismic sources number of receivers vertical stacking and noise conditions for a known reference reflector at 2 66 km depth at a geothermal site in northern germany the results of a simple surface seismic experiment were therefore combined with numerical forward modeling for different injection scenarios at 3 8 km depth the underlying idea is that changes of reflectivity from the injection at 3 8 km must be larger than the variance of the measurements to be observable assuming that the injection at 3 8 km depth would produce a subhorizontal disklike target with a fracture porosity of 2 or 5 the critical porosity the water injection volume has to be at least 443 and 115 m 3 respectively to be detectable from the surface if the injection on the other hand does not create subhorizontal but subvertical pathways or only reduces the seismic velocities via the increased pore pressure in the immediate vicinity of the bore hole the injection is undetectable from the surface the most promising approach is therefore to move sources and or receivers closer to the target that is the use of borehole instrumentation

glacial water mass geometry and the distribution of δ13c of σco2 in the western atlantic ocean 1 oxygen and carbon isotopic data were produced on the benthic foraminiferal taxa cibicidoides and planulina from 25 new piston cores gravity cores and multicores from the brazil margin the cores span water depths from about 400 to 3000 m and intersect the major water masses in this region these new data fill a critical gap in the south atlantic ocean and provide the motivation for updating the classic glacial western atlantic 13c transect of duplessy et al 1988 the distribution of 13c of co2 requires the presence of three distinct water masses in the glacial atlantic ocean a shallow 1000 m southern source water mass with an end member 13c value of about 0 3 0 5 vpdb a middepth 1500 m northern source water mass with an end member value of about 1 5 and a deep 2000 m southern source water with an end member value of less than 0 2 and perhaps as low as the 0 9 values observed in the south atlantic sector of the southern ocean ninnemann and charles 2002 the origins of the water masses are supported by the meridional gradients in benthic foraminiferal 18o a revised glacial section of deep water 13c documents the positions and gradients among these end member intermediate and deep water masses the large property gradients in the presence of strong vertical mixing can only be maintained by a vigorous overturning circulation

pressure and fluid saturation prediction in a multicomponent reservoir using combined seismic and electromagnetic imaging this paper presents a method for combining seismic and electromagnetic em measurements to predict changes in water saturation pressure and co2 gas oil ratio in a reservoir undergoing co2 flood crosswell seismic and em data sets taken before and during co2 flooding of an oil reservoir are inverted to produce crosswell images of the change in compressional velocity shear velocity and electrical conductivity during a co2 injection pilot study a rock properties model is developed using measured log porosity fluid saturations pressure temperature bulk density sonic velocity and electrical conductivity the parameters of the rock properties model are found by an l1 norm simplex minimization of predicted and observed differences in compressional velocity and density a separate minimization using archie s law provides parameters for modeling the relations between water saturation porosity and electrical conductivity the rock properties model is used to generate relationships between changes in

multispecies approach to reconstructing eastern equatorial pacific thermocline hydrography during the past 360 kyr 1 stable isotope data from eastern equatorial pacific eep core tr163 19 2 15 n 90 57 w 2348 m are presented for the surface dwelling foraminifers globigerinoides ruber and g sacculifer and thermocline dwelling globorotalia menardii and neogloboquadrina dutertrei using species specific normalization factors derived from experimental and plankton tow data we reconstruct a 360 kyr record of water column hydrography across the past three glacial cycles we demonstrate that g ruber maintains a mixed layer habitat throughout the entire record while g sacculifer records a mixture of thermocline and mixed layer conditions and g menardii and n dutertrei record thermocline properties we conclude that g sacculifer is not appropriate for paleoceanographic applications in regions with steep vertical hydrographic gradients results suggest that this region of the eep had a thicker mixed layer and deeper 13cdic boundary between the surface and equatorial undercurrent during the last two glacial periods a shift in n dutertrei and g sacculifer geochemistry prior to 185 kyr suggests water column structure and chemocline gradients changed possibly due to a shift in the position of the undercurrent relative to this site the timing and magnitude of glacial interglacial 13c variations between species indicates that near surface carbon chemistry is controlled by changes in productivity atmospheric circulation and advected intermediate water sources north of the antarctic polar front these results demonstrate that when properly calibrated for species differences multispecies geochemical data sets can be invaluable for reconstructing water column structure and properties in the past

time lapse crosswell seismic tomography to characterize flow structure in the reservoir during the thermal stimulation time lapse crosswell seismic tomography data recorded with an interval of six months indicate a strong directional thermal response in a fractured eolian sandstone reservoir at a five spot thermal stimulation site in the south casper creek oil field wyoming the seismic thermal response depicted on the tomogram and in conjunction with the geological data from cores and a wireline log reveals the multichannel flow mechanism in the reservoir formation the three factors that control steam or heat propagation are the fractures the directional permeability existing in the rock matrix and the fault crosswell tomograms imply that the primary fluid flow is through fractures oriented north south whereas the secondary fluid flow is through the matrix in the direction of maximum horizontal permeability the thermal response expressed on the tomogram infers that a fault oriented n80 degrees e offsets flow units and acts as a flow barrier or baffle the flow structure implied by the crosswell seismic tomography is strikingly different from the initial conjecture as deduced from engineering perception based on geological reasoning however the tomographic implications were supported by both a tracer test and fluid temperature measurements at the four producing wells around the injector

dilution of the northern north atlantic ocean in recent decades declining salinities signify that large amounts of fresh water have been added to the northern north atlantic ocean since the mid 1960s we estimate that the nordic seas and subpolar basins were diluted by an extra 19 000 5000 cubic kilometers of freshwater input between 1965 and 1995 fully half of that additional fresh water about 10 000 cubic kilometers infiltrated the system in the late 1960s at an approximate rate of 2000 cubic kilometers per year patterns of freshwater accumulation observed in the nordic seas suggest a century time scale to reach freshening thresholds critical to that portion of the atlantic meridional overturning circulation

time lapse velocity analysis application to onshore continuous reservoir monitoring in 4d seismic the velocity model used for imaging and reservoir characterization can change as production from the reservoir progresses this is particularly true for heavy oil reservoirs stimulated by steam injection in the context of sparse and low fold seismic acquisitions conventional migration velocity analyses can be inadequate because of a poorly and irregularly sampled offset dimension we propose to update the velocity model in the context of daily acquisitions with buried sources and receivers the main objective is to demonstrate that subtle time lapse effects can be detected over the calendar time on onshore sparse acquisitions we introduce a modified version of the conventional prestack time migration to detect velocity changes obtained after cross correlation of the base and monitor surveys this technique is applied on a heavy oil real data set from the netherlands and reveals how the steam diffuses over time within the reservoir

utilizing the onset of time lapse changes a robust basis for reservoir monitoring and characterization time lapse monitoring is useful for imaging changes in geophysical attributes due to fluid flow in trying to use time lapse data for reservoir characterization difficulties often arise when relating changes in geophysical observations to changes in fluid saturation and pressure as an alternative approach for reservoir monitoring and characterization we introduce the idea of an onset time the time at which a measured quantity such as a seismic traveltime or a reflection amplitude begins to deviate from its background value we illustrate the idea and demonstrate its utility through the consideration of traveltimes recorded by the continuous active source seismic monitoring system at the frio pilot site near houston texas the system which transmits an elastic wave every 15 min is used to monitor the movement of carbon dioxide injected into a permeable sand formation from these data we can estimate the onset of changes in seismic traveltimes to six receivers in an adjacent borehole numerical simulation and synthetic tests indicate that the onset times are not very sensitive to the method used to compute the effective fluid bulk modulus and correspondingly the seismic compressional velocity rather the onset times are strongly influenced by saturation changes within the formation specifically by the break through time of the injected fluid phase by means of an iterative inversion algorithm we use the onset times to estimate permeability variations between the boreholes at the frio pilot site the authors 2014 published by oxford university press on behalf of the royal astronomical society

millennial scale sea surface temperature variability in the western tropical north atlantic from planktonic foraminiferal census counts planktonic foraminiferal census counts are used to construct high resolution sea surface temperature sst and subsurface thermocline temperature records at a core site in the tobago basin lesser antilles the record is used to document climatic variability at this tropical site in comparison to middle and high latitude sites and to test current concepts of cross equatorial heat transports as a major player in interhemispheric climate variability temperatures are estimated using transfer function and modern analog techniques glacial maximum cooling of 2 5 3 c is indicated maximum cooling by 4 c is inferred for isotope stage 3 the sst record displays millennial scale variability with temperature jumps of up to 3 c and closely tracks the structure of ice core dansgaard oeschger cycles sst variations in part of the record run opposite to the sst evolution at high northern latitude sites pointing to thermohaline circulation and marine heat transport as an important factor driving sst in the tropical and high latitude atlantic both on orbital and suborbital timescales

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

evidence for calcification depth change of globorotalia truncatulinoides between deglaciation and holocene in the western atlantic ocean abstract measurements of the 18o in tests of planktonic and benthic foraminifera in the florida straits are used to reconstruct the properties of the water column through time over the last 12 ka lynch stieglitz et al in press the isotopic composition of the foraminifera largely reflects the vertical density gradient we use this reconstruction and 18o measurements on globorotalia truncatulinoides in a nearby core to track the depth habitat of this species from the last deglaciation to 1 6 ka b p around 9 ka g truncatulinoides was calcifying in much shallower water than during the late holocene the downward migration toward its modern habitat is a regional phenomenon over the western tropical atlantic continental slope the cause is still unclear but we hypothesize that the shallower calcification depth may be a response to the presence of glacial melt water or to circulation changes this study points to the value of further study of the ecology life cycle and calcification depth for g truncatulinoides and other planktonic foraminifera that are used to reconstruct the history of the thermocline and upper water column structure

elastic anisotropy due to aligned cracks in porous rock all theoretical expressions which relate the characteristics of saturated aligned cracks to the associated elastic anisotropy are restricted in some important way for example to the case of stiff pore fluids or of the absence of equant porosity or of a moderately high frequency band because of these restrictions previous theory is not suitable for application to the upper crust where the pore fluid is brine kf k820 the equant porosity is often substantial p 0 1 and the frequency band is sonic to seismic this work removes these particular restrictions recognizing in the process an important mechanism of dispersion a notable feature of these more general expressions is their insensitivity at low frequency to the aspect ratio of the cracks only the crack density is critical an important conclusion of this more general model is that many insights previously achieved concerning the shear wave splitting due to vertical aligned saturated cracks are sustained however conclusions on crack orientation or crack aspect ratio which were derived from p wave data or from shear wave critical angles may need to be reconsidered further the non linear coupling between pores and cracks due to pressure equalization effects means that the linear schoenberg muir calculus may not be applied to such systems the theory receives strong support from recent data by rathore et al on artificial samples with controlled crack geometry

weaker gulf stream in the florida straits during the last glacial maximum as it passes through the florida straits the gulf stream consists of two main components the western boundary flow of the wind driven subtropical gyre and the northward flowing surface and intermediate waters which are part of the global conveyor belt compensating for the deep water that is exported from the north atlantic ocean1 the mean flow through the straits is largely in geostrophic balance and is thus reflected in the contrast in seawater density across the straits2 here we use oxygen isotope ratios of benthic foraminifera which lived along the ocean margins on the boundaries of the florida current during the last glacial maximum to determine the density structure in the water and thereby reconstruct transport through the straits using the geostrophic method a technique which has been used successfully for estimating present day flow3 our data suggest that during the last glacial maximum the density contrast across the florida straits was reduced with the geostrophic flow referenced to the bottom of the channel at only about two thirds of the modern value if the wind driven western boundary flow was not lower during the last glacial maximum than today these results indicate a significantly weaker conveyor belt component of the gulf stream compared to present day values whereas previous studies based on tracers suggested that deep waters of north atlantic origin were not widespread during glacial times indicating either a relatively weak or a shallow overturning cell our results provide evidence that the overturning cell was indeed weaker during glacial times

evidence from the high latitude north atlantic for variations in antarctic intermediate water flow during the last deglaciation we present evidence that the characteristic chemical signature based on coupled benthic foraminiferal cd ca and d13c of antarctic intermediate waters aaiw penetrated throughout the intermediate depths of the atlantic basin to the high latitude north atlantic during the abrupt cooling events of the last deglaciation heinrich 1 and the younger dryas aaiw may play the dynamic counterpart to the bipolar seesaw when near freezing salty bottom waters from the antarctic aabw sluggishly ventilate the deep ocean our data reinforce the concept that interglacial circulation is stabilized by salinity feedbacks between salty northern sourced deep waters nadw and fresh southern sourced waters aabw and aaiw further the glacial ocean may be susceptible to the more finely balanced relative densities of nadw and aaiw due to either freshwater input or a reversal of the salinity gradient such that the ocean is poised for nadw collapse via a negative salinity feedback the unstable climate of the glacial period and its termination may arise from the closer competition for ubiquity at intermediate depths between northern and southern sourced intermediate waters

the oldest south american cricetidae rodentia and mustelidae carnivora late miocene faunal turnover in central argentina and the great american biotic interchange abstract the discovery of a rich fauna from the late miocene cerro azul formation in caleufu central argentina is reported this fauna includes vertebrate holarctic immigrants among which are the oldest south american records of mammals of the families cricetidae rodentia and mustelidae carnivora stratigraphic biochronological and taphonomic evidence indicates that the faunal assemblage from caleufu is confidently synchronous and represents the late huayquerian zone of xenodontomys elongatus late miocene thus this fauna supports hypotheses of the arrival of cricetids and mustelids prior to the pliocene completion of the panamanian isthmus however the new records do not permit inferences to be made about precise moments of entry of these groups into south america representation of the gabi in the fossil record is here interpreted as a major event integrated by a nested pattern of events including geographically more restricted turnovers implying particular taphonomic and geographic biases and associated environmental changes in such a hierarchical context the record of caleufu represents a local turnover different from those occurring with arrivals of these taxa or their ancestors into the continent in accordance with biochronological data the turnover recorded in caleufu could be coeval with the global scale glacial event detected for the late miocene ca 5 7 5 8 ma in southern south america this arid and cold pulse would have triggered the distribution drift to central argentina of fauna previously restricted to western peri andean areas local turnovers such as the one reported here and associated physical changes have to be analyzed in detail as individual events in order to interpret the chronology dynamics and paleoenvironmental context of hierarchically greater episodes such as the gabi

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

crosswell electromagnetic and seismic imaging an examination of coincident surveys at a steam flood project we studied crosswell electromagnetic and seismic images of three oil saturated intervals within a southern california heavy oil field undergoing steam flood the crosswell survey is located in a portion of the field where one well is in a cold spot resulting in differing steam propagation within the three units log analysis shows linear or second order polynomial relationships with correlation coefficients greater than 0 7 between electrical conductivity and water saturation porosity and clay content whereas only a weakly linear relationship can be found between velocity and temperature in the lower unit studied crosswell seismic data is used to produce a velocity tomogram and a reflection section and crosswell electromagnetic data is used to produce a conductivity section and derived porosity and water saturation the seismic velocities from the tomograms show lateral variations consistent with the lateral variations in temperature seen in observation wells on either side of the crosswell sect

a geostatistical framework for incorporating seismic tomography auxiliary data into hydraulic conductivity estimation abstract a geostatistical approach is presented for the inclusion of seismic tomography data and sonic log data into the estimation of hydraulic conductivity the procedure accounts for the errors in seismic tomography inversion and for the correlation of such errors the proposed methodology consists of two steps 1 the cross variogram inference is carried out using only the data at the wellbore both hydraulic and seismic 2 a co kriging procedure takes the cross well data into account to interpolate between boreholes no postulated a priori relationship is needed in order to illustrate the methodology a synthetic data set is generated on the basis of evidence from published case studies and simplified physical considerations the numerical experiments show that the choice of the excitation frequency is critical a trade off exists between the need for a high resolution survey asking for higher frequencies and the need for a good correlation between hydraulic conductivity and seismic properties asking for frequencies below the squirt frequency of the medium in the simulation using seismic data with the best excitation frequency 1 khz in this case the mean squared error of the hydraulic conductivity estimate is two thirds lower than using hydraulic data alone it is important to note also that only a part of the interwell region is adequately sampled by the tomographic experiment such a region can be readily identified by calculating the energy of the quasi null space through singular value decomposition of the tomographic matrix in planning this type of experiments it is necessary to carefully verify case by case whether the adopted range of high frequencies does not prevent the seismic energy from propagating effectively from sources to receivers

deglacial variability in the surface return flow of the atlantic meridional overturning circulation 1 benthic foraminiferal cd ca from a florida current sediment core documents the history of the northward penetration of southern source waters within the surface return flow of the atlantic meridional overturning circulation amoc cd seawater estimates cdw indicate that intermediate depth southern source waters crossed the equator and contributed to the florida current during the bolling allerod warm period of the last deglaciation consistent with evidence of only a modest amoc reduction compared to today the cdwestimates also provide the first paleoceanographic evidence of a reduction in the influence of intermediate depth southern source waters within the florida current during the younger dryas a deglacial cold event characterized by a weak north atlantic amoc our results reveal a close correspondence between the northward penetration of intermediate depth southern source waters and the influence of north atlantic deep water suggesting a possible link between intermediate depth southern source waters and the strength of the atlantic amoc

a high resolution late quaternary upwelling record from the anoxic cariaco basin venezuela results are presented of a high resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the cariaco basin in the southern caribbean sea the cariaco basin is a small anoxic marine basin on the northern continental margin of venezuela in an area today characterized by both seasonal trade wind induced upwelling and pronounced dry and wet seasons our data indicate that large changes in the intensity of upwelling and hence trade wind strength occurred in this region during the last glacial interglacial transition and throughout the holocene during the last glacial lowstand of sea level the cariaco basin was effectively isolated from the open caribbean along its northern margin by the then largely emergent tortuga bank oxic conditions existed in the deep cariaco basin at this time and surface productivity was low about 12 600 years ago the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the laurentide ice sheet into the gulf of mexico strong upwelling between 12 600 and about 10 000 years ago may be related to intensified trade winds resulting in part from cooler sea surface temperatures in the caribbean and gulf of mexico after about 10 000 years ago upwelling intensity was reduced though highly variable a preliminary frequency domain analysis of the holocene portion of the cariaco basin time series suggests that solar forcing may explain a significant component of the century scale variability observed in the record of upwelling and trade wind strength