reservoir compartmentalization an introduction reservoir compartmentalization the segregation of a petroleum accumulation into a number of individual fluid pressure compartments occurs when flow is prevented across sealed boundaries in the reservoir these boundaries are caused by a variety of geological and fluid dynamic factors but there are two basic types static seals that are completely sealed and capable of withholding trapping petroleum columns over geological time and dynamic seals that are low to very low permeability flow baffles that reduce petroleum crossflow to infinitesimally slow rates the latter allow fluids and pressures to equilibrate across a boundary over geological time scales but act as seals over production time scales because they prevent crossflow at normal production rates such that fluid contacts saturations and pressures progressively segregate into dynamic compartments thus reservoir compartmentalization impacts the volume of moveable produceable oil or gas that might be connected to any given well drilled in a field which restricts the volume of reserves that can be booked for that field booking of reserves is tightly regulated by government authorities because it is a key measure used by stock analysts and investors to value an oil company this places reservoir compartmentalization studies and the predictive science and technology applied to them at the heart of company valuation unexpected compartmentalization can also seriously impact the profitability of a field with more data acquisition more study more wells more time being required to produce less oil and gas than was originally anticipated in extreme cases this might even lead to early field abandonment however unexpected or misunderstood reservoir compartmentalization has been an industrywide experience for over 30 years and it is clear that there is great value in learning from past often expensive mistakes e g smith 2008 this learning process has often driven developments in geoscience engineering and related technology enabling operating companies to identify and predict new untapped volumes in old fields make general improvements to field management e g gainski et al wonham et al and apply this knowledge to other similar but lessmature fields in their portfolio reservoir compartmentalization is therefore a major uncertainty that should be accurately assessed during the appraisal of petroleum reservoirs in order to avoid unexpected compartmentalization at the production stage in the past few decades there have been major advances in data detection and surveillance methods and our geoscience and reservoir engineering approaches however reservoir compartmentalization can still be underestimated during field appraisal and can still give surprises that force a re think of the field development and production plan e g smith 2008 this is not necessarily a defect in the science or technology but rather it may also be a result of ineffectual data appraisal or discipline integration within subsurface workflows thus it is not unusual for subsurface teams to place too much emphasis on one aspect of the evidence or to make early assumptions that bias data acquisition analyses and interpretations later on for example fisher jolley 2007 point out that non existent faults or improbable fault seal capacities might be invoked to explain variable petroleum contacts and dynamic fluid pressure behaviour when an alternative or combination of factors or other unrelated explanations might be more appropriate for the data e g hydrodynamic tilting of petroleum contacts tozer borthwick research initiatives and collaborations between oil companies service groups and academic institutions vary considerably in scope and content and there is often a creative tension between the competitive advantages motivations and knowledge gaps perceived by the sponsoring companies and their research partners in addition to this the scientific insights that can be gained from the

the development of a long range foraminifer transfer function and application to late pleistocene north atlantic climatic extremes north atlantic transfer function gsf18 was developed from simplified core top planktic foraminifer census data simplifications are based upon similar environmental responses of some modern taxa and assumptions about the paleoecology of now extinct pliocene taxa gsf18 is evaluated through application to time slice data sets from the last glacial maximum 18 ka and last interglacial 122 ka of the north atlantic ocean quantitative sea surface temperature estimates from gsf18 at 106 glacial sites and 18 interglacial sites are approximately equivalent to climate long range investigation mapping and prediction climap results at the same sites a glacial north atlantic considerably cooler than modern conditions and a last interglacial north atlantic approximately the same as or slightly warmer than modern conditions minor differences are explained by the taxonomic structure of gsf18 and provide further insight into the environmental and temporal robustness of the transfer function

geomechanical response to seasonal gas storage in depleted reservoirs a case study in the po river basin italy 1 underground gas storage ugs in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand and occurs in many places in europe and north america in response to summer gas injection and winter gas withdrawal the reservoir expands and contracts essentially elastically as a major consequence of the fluid gas and water pore pressure fluctuations depending on a number of factors including the reservoir burial depth the difference between the largest and the smallest gas pore pressure and the geomechanical properties of the injected formation and the overburden the porous medium overlying the reservoir is subject to three dimensional deformation with the related cyclic motion of the land surface being both vertical and horizontal we present a methodology to evaluate the environmental impact of underground gas storage and sequestration from the geomechanical perspective particularly in relation to the ground surface displacements long term records of injected and removed gas volume and fluid pore pressure in the lombardia gas field northern italy are available together with multiyear detection of vertical and horizontal west east displacement of the land surface above the reservoir by an advanced permanent scatterer interferometric synthetic aperture radar psinsar analysis these data have been used to calibrate a 3 d fluid dynamic model and develop a 3 d transversally isotropic geomechanical model the latter has been successfully implemented and used to reproduce the vertical and horizontal cyclic displacements on the range of 8 10 mm and 6 8 mm respectively measured between 2003 and 2007 above the reservoir where a ugs program has been underway by stogit eni s p a since 1986 following a 5 year field production life because of the great economical interest to increase the working gas volume as much as possible the model addresses two ugs scenarios where the gas pore overpressure is pushed from the current 103 pi where pi is the gas pore pressure prior to the field development to 107 pi and 120 pi results of both scenarios show that there is a negligible impact on the ground surface with deformation gradients that remain well below the most restrictive admissible limits for the civil structures and infrastructures

a geomechanical transversely isotropic model of the po river basin using psinsar derived horizontal displacement abstract hydrocarbon production co 2 subsurface sequestration and gas storage in exhausted reservoirs are a few anthropogenic activities involving the extraction or injection of fluids underground as a consequence the withdrawn injected formation undergoes an effective stress change that may induce deep deformations propagating to the ground level with possible fault re activations the geomechanical parameters needed to simulate and predict the above processes can also be indirectly inferred by interferometric synthetic apertur radar insar based techniques that are used to monitor the land surface displacements in the present study the insar measurements above two exhausted fields of the po river plain italy presently employed for seasonal gas storage are used to develop set up and calibrate a transversely isotropic geomechanical model of the porous medium it is shown that only assuming transverse isotropy allows for a satisfactory reproduction of both the vertical and horizontal displacements that cannot be simultaneously matched by a simpler isotropic model moreover similar parameters prove correct for both the reservoirs located about 30 km apart providing evidence of the regional range of the above model applicability

linking reservoir geomechanics and time lapse seismics predicting anisotropic velocity changes and seismic attributes seismic technology has been used successfully to detect geomechanically induced signals in repeated seismic experiments from more than a dozen fields to explain geomechanically induced time lapse 4d seismic signals we use results from coupled reservoir and geomechanical modeling the coupled simulation yields the 3d distribution over time of subsurface deformation and triaxial stress state in the reservoir and the surrounding rock predicted changes in triaxial stress state are then used to compute changes in anisotropic p and s wave velocities employing a stress sensitive rock physics transform we predict increasing vertical p wave velocities inside the reservoir accompanied by a negative change in p wave anisotropy e 0 a stress sensitive rock physics transform that predicts a

late quaternary coccoliths at the north pole evidence of ice free conditions and rapid sedimentation in the central arctic ocean calcareous nannofossils from approximately the past 7000 yr of the holocene and from oxygen isotope stage 5 are present at 39 analyzed sites in the central arctic ocean this indicates partly ice free conditions during at least some summers the depth of holocene sediments in the nansen basin is about 20 cm or more where influenced by turbidites on the gakkel ridge calcite preservation is excellent and holocene strata are consistently documented to be at least 4 to 20 cm thick in the amundsen basin preservation of nannofossils is sometimes poor holocene specimens are commonly only found at the surface although at one site they extend down to 26 cm the holocene assemblage is consistently recorded in the upper 5 to 20 cm of sediment on the lomonosov ridge and down to 15 cm depth in the makarov basin this implies that linear sedimentation rates for the holocene in all investigated areas are centimetres per thousand years sediments from the last glacial period oxygen isotope stages 2 4 are relatively thin suggesting significantly reduced sedimentation millimetres per thousand years during this time

an early to mid pleistocene deep arctic ocean ostracode fauna with north atlantic affinities abstract an early to middle pleistocene ostracode fauna was discovered in sediment core p1 93 ar 23 p23 76 95 n 155 07 w from 951 meter water depth from the northwind ridge western arctic ocean piston core p23 yielded more than 30 000 specimens and a total of about 30 species several early to mid pleistocene species in the genera krithe echinocythereis pterygocythereis and arcacythere are now extinct in the arctic and show taxonomic affinities to north atlantic ocean species our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the mid pleistocene transition mpt 1 2 to 0 7 ma and the mid brunhes event mbe 400 ka reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400 000 years

rocks under strain strain induced time lapse time shifts are observed for depleting reservoirs pressure depletion as a result of oil and gas production creates changes in the stress and strain fields of the rock material both inside and outside the reservoir seismic waves propagating through these rocks have different traveltimes before and after depletion because the layer thicknesses change and the seismic velocity is altered by the changes in the stress and strain fields the cumulative change in two way traveltimes with depth is referred to as time lapse time shift

water masses and circulation in the eurasian basin results from the oden 91 expedition the oden 91 north pole expedition obtained oceanographic measurements on four sections in the nansen and amundsen basins of the eurasian basin and in the makarov basin of the canadian basin thereby proving the feasibility of carrying out a typical oceanographic program using an icebreaker in the arctic ocean the data show greater spatial variability in water structure and circulation than was apparent from previous data the results show that a clear front exists between the eurasian and canadian basins such that upper halocline water in the canadian basin is almost absent from the eurasian basin the lower halocline water produced in the barents kara sea region permeates much of the eurasian basin and flows along the continental slope into the canadian basin the deeper circulation is strongly influenced by topography three return flows of the atlantic layer are identified one over the nansen gakkel ridge one over the lomonosov ridge and a third flowing from the canadian basin the slight differences observed in salinity and temperature characteristics of the deeper waters of the nansen and amundsen basins do not lead to an obvious explanation of their origin or flow pattern

benthic ostracoda in the benguela system se atlantic a multivariate analysis abstract q mode factor analysis of ostracod faunas from 127 modern sediment samples associated with the benguela system over the continental margin off namibia and south africa identifies ten factor associations of species fa these fa account for 93 of the variance and can be related to nine sea bottom variables temperature salinity dissolved oxygen total orgainc matter elemental iron terrigenous component calcium carbonate glauconite sand and mud transfer functions for these variables are calculated for future palaeo environmental analyses on the modern continental slope fahenryhowella melobesioides andkrithe capensis are controlled primarily by cross shelf temperature gradients while on the uppermost slope and outer shelf dissolved oxygen values restrict the distribution of facytherella namibensis oxygen depleted andruggieria cytheropteroides normal oxygen levels in the north and south respectively inner and middle shelf faunal associations are controlled by high salinities north of 26 s fapalmoconcha walvisbaiensis while substrate variables terrigenous glauconite mud and organic matter are the main determinants farther south fabensonia knysnaensis knysnaensis pseudokeijella lepralioides bairdoppilata simplex ambostracon keeleri flabellicostata andparacypris lacrimata these faunal hydrographic relationships are linked to various dynamic oceanographic features such as upwelling cross shelf advection and shelf parallel bottom currents

comparative ecological analysis of the ostracod faunas from low and high polluted southwestern spanish estuaries a multivariate approach abstract the distribution and abundance of both living and total ostracod populations from the estuaries of the southwestern spanish coast are discussed a total of 68 species were obtained from 120 bottom samples collected in the channels channel margins and salt marshes four assemblages were recognized in this area a urocythereis oblonga assemblage with marine species well represented in sandy substrates located near the mouths b loxoconcha rhomboidea assemblage mainly developed in the quiet tidal channels conected with the main channels of the marine domains c loxoconcha elliptica assemblage enclosing the most cosmopolitan and euryhaline species very abundant in muddy sediments and low to moderate hydrodynamic conditions and d leptocythere porcellanea assemblage only observed in the clayey silty channel margins of the most protected ebb channels in these transitional environments very unfavorable conditions for the ostracod development were found in a the erosional channels and channel margins b most of the salt marsh samples with high subaerial exposure and c sectors with high metallic pollution levels and acidic waters

mapping eastern north american vegetation change of the past 18 ka no analogs and the future the method of modern analogs and an extensive data base of modern and fossil pollen data were used to generate a new series of paleovegetation maps for eastern north america spanning the past 18 ka the maps illustrate the continuous nature of climate induced vegetation change and the development after about 10 ka of modern regional vegetation patterns before the holocene vegetation biomes without modern analogs were widespread in response to climate conditions without modern analogs and to a lesser extent to the rapidity of climate change over the last glacial interglacial transition this geological perspective suggests that possible future climate changes could force similarly complex changes in natural vegetation including the development of biomes without modern analogs

postglacial to holocene history of the laptev sea continental margin palaeoenvironmental implications of benthic assemblages abstract bivalves ostracods and foraminifers were studied in four ams 14 c dated sediment cores from the laptev sea one from the upper continental slope with a date of 15 8 cal ka in its basal part and three from river palaeovalleys on the outer middle shelf aging back to 12 7 11 2 cal ka at the continental margin high relative proportions of cassidulina neoteretis planktic foraminifers and ostracods with north atlantic affinities provide evidence on past inflows of atlantic derived waters whereas freshwater inputs downslope sediment movements and ice rafting are documented by the presence of euryhaline brackish water and freshwater ostracods and low planktic benthic ratio atlantic derived subsurface waters reached the studied site by ca 16 cal ka i e prior to the establishment of the pathway across the barents sea shelf further west the strongest atlantic influence occurred prior to 12 cal ka and after 3 cal ka a cold low nutrient marine environment with a coastal polynya setting is reconstructed for the time 16 14 cal ka whereas between 12 7 and 11 2 cal ka freshwater influence reached its maximum during a time when the outer shelf was flooded and brackish water assemblages inhabited the estuarine parts of palaeovalleys following the temporal and spatial pattern of sea level rise these fluvially affected assemblages rapidly transformed into shallow marine faunas after ca 3 5 3 cal ka well pronounced changes in the benthic communities indicate a general climate cooling characterized by a more intensified surface and bottom water circulation regime

ostracod faunas and water masses across the continental margin off southwestern africa changes in composition of modern benthic ostracod faunas across the continental margin of southwestern africa occur at boundaries between and within major water masses a mixed layer antarctic intermediate water aaiw boundary at 200 m an aaiw salinity minimum zone at 650 m an aaiw bathyal thermocline at 1000 m and the aaiw north atlantic deep water nadw boundary at 1500 m in addition two population changes occur within the nadw at 1 8 2 0 km and 2 0 3 0 km the antarctic bottom water assemblage is sparse and poorly preserved

reconstructing late quaternary deep water masses in the eastern arctic ocean using benthonic ostracoda abstract the distribution of ostracoda in three long cores from the deep eastern arctic ocean was studied to determine the palaeoceanographical history of the eurasian basin during the late quaternary the samples for this study were obtained from the lomonosov ridge morris jesup rise and yermak plateau during the arctic 91 expedition ostracoda previously studied in coretops at the same sites as the present study have shown that individual species have a strong association with different water masses and bathymetry throughout the late quaternary cores exhibit ostracod rich layers separated by barren intervals on the basis of biostratigraphical isotopic and palaeomagnetic data the fossiliferous levels are interpreted as representing interglacial stages the twenty most significant species were selected for subsequent quantitative investigation using cluster and factor analyses in order to determine similarity and variance between the assemblages an additional statistical method employing modern analogues and the squared chord distance dissimilarity coefficient was utilised to compare the present late quaternary fossil samples with a modern arctic database the results reveal a major faunal division within the arctic ocean deep water aodw highly abundant and diverse assemblages within the cores were found to group and have good analogues with the recent bathyal depth 1000 2500 m upper aodw assemblages conversely assemblages with low abundance and diversity correlate well with abyssal depth 3000 m lower aodw assemblages the palaeoceanographical history is complicated by the influence of adjacent water masses such as canada basin deep water cbdw greenland sea deep water gsdw and most importantly arctic intermediate water aiw which all had an influence on the ostracod assemblages during the late quaternary an enhanced flow of warm saline aiw into the eurasian basin results in species rich upper aodw assemblages having good analogues down to 2750 m in the water column in contrast lower aodw assemblages influenced by cold well oxygenated gsdw give analogues at depths as shallow as 1000 m the faunal changes are the consequence of rapid climatic fluctuations in the eastern arctic ocean during the late quaternary that are intrinsically linked to palaeoceanographical alternations in warm and cold current inflow from adjacent basins

the 7 may 2001 induced seismic event in the ekofisk oil field north sea 1 a moderate size seismic event on 7 may 2001 was strongly felt on platforms in the ekofisk oil field in the southern north sea but did not cause damage to platforms or wells we combined near and far field observations to develop a consistent source model and to determine whether the event was induced seismic data placed the epicenter inside the ekofisk field and suggested a shallow source depth based on spectral and moment tensor analysis gps data from the ekofisk platforms displayed permanent vertical and horizontal movement due to the event a topographic bulge in the sea bottom revealed by differential bathymetry data and overpressure in the overburden in the northeastern part of the field detected only after the event had been caused by unintentional water injection that started in 1999 the injection pressure and rate were sufficient to raise the overburden pressure gauge and compaction data ruled out that the event occurred at reservoir level which was further supported by unaffected production rates and absence of well failure we therefore conclude that the event occurred in the overburden at less than 3 km depth initially this appeared unlikely on account of very low shear strength of the overburden clay rich shale and mud rocks the seismic event was induced owing to stress changes caused by water injection the event possibly initiated on the northern flank of the field near the water injector and may have involved flexure of the overburden into the depression bowl in the rest of the field moment tensor analysis is consistent with a pure double couple source we suggest that slip occurred on the near horizontal rather than along the near vertical nodal plane stress drop was low and owing to the low overburden shear strength the event released less energy than a typical stress drop event with similar source dimensions

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

basin scale compressibility of the northern adriatic by the radioactive marker technique the paper presents a constitutive model for the one dimensional vertical compressibility mv of the northern adriatic sedimentary basin based on in situ deformation measurements by the radioactive marker technique gas reservoir compaction and expansion occurring during the field production life and after its abandonment have been measured in three deep boreholes of the northern adriatic by fsmt formation subsidence monitoring tool and cmi compaction monitoring instrument developed by schlumberger and western atlas respectively the compressibility values as obtained by relating the shortening of the distance between several pairs of adjacent markers to the pore pressure decline experienced by the productive levels during the monitored time interval are statistically processed to reduce the influence of operational and instrumental errors the method of moving weighted averages is used over clustered depth intervals the compressibility thus derived is related to the in situ vertical effective stre

evidence of regional subsidence and associated interior wetland loss induced by hydrocarbon production gulf coast region usa analysis of remote images elevation surveys stratigraphic cross sections and hydrocarbon production data demonstrates that extensive areas of wetland loss in the northern gulf coast region of the united states were associated with large volume fluid production from mature petroleum fields interior wetland losses at many sites in coastal louisiana and texas are attributed largely to accelerated land subsidence and fault reactivation induced by decreased reservoir pressures as a result of rapid or prolonged extraction of gas oil and associated brines evidence that moderately deep hydrocarbon production has induced land surface subsidence and reactivated faults that intersect the surface include 1 close temporal and spatial correlation of fluid production with surficial changes including rapid subsidence of wetland sediments near producing fields 2 measurable offsets of shallow strata across the zones of wetland loss 3 large reductions in subsurface pressures where subsidence rates are high 4 coincidence of orientation and direction of displacement between surface fault traces and faults that bound the reservoirs and 5 accelerated subsidence rates near producing fields compared to subsidence rates in surrounding areas or compared to geological rates of subsidence based on historical trends subsidence rates in the gulf coast region near producing fields most likely will decrease in the future because most petroleum fields are nearly depleted alternatively continued extraction of conventional energy resources as well as potential production of alternative energy resources geopressured geothermal fluids in the gulf coast region could increase subsidence and land losses and also contribute to inundation of areas of higher elevation

thermohaline circulation in the arctic mediterranean seas the renewal of the deep north atlantic by the various overflows of the greenland scotland ridges is only one manifestation of the convective and mixing processes which occur in the various basins and shelf areas to the north the arctic ocean and the greenland iceland and norwegian seas collectively called the arctic mediterranean the traditional site of deep ventilation for these basins is the greenland sea but a growing body of evidence also points to the arctic ocean as a major source of deep water this deep water is relatively warm and saline and it appears to be a mixture of dense brine enriched shelf water with intermediate strata in the arctic ocean the deep water exits the arctic ocean along the greenland slope to mix with the greenland sea deep water conversely very cold low salinity deep water from the greenland sea enters the arctic ocean west of spitsbergen within the arctic ocean the lomonosov ridge excludes the greenland sea deep water from the canadian basin leaving the latter warm saline and rich in silica in general the entire deep water sphere of the arctic mediterranean is constrained by the greenland scotland ridges to circulate internally therefore it is certain of the intermediate waters formed in the greenland and iceland seas which ventilate the north atlantic these waters have a very short residence time in their formation areas and are therefore able to rapidly transmit surface induced signals into the deep north atlantic

a quantitative micropaleontologic method for shallow marine peleoclimatology application to pliocene deposits of the western north atlantic ocean abstract a transfer function was developed to estimate summer and winter paleotemperatures for arctic to tropical regions of the western north atlantic ocean using fossil ostracode assemblages q mode factor analysis was run on ostracode assemblages from 100 modern bottom sediment samples from continental shelves of north america greenland and the caribbean using 59 ostracode taxa seven factors accounting for 80 of the variance define assemblages that correspond to frigid subfrigid cold temperate mild temperate warm temperate subtropical and tropical climatic zones multiple regression of the factor matrix against observed february and august bottom temperatures yielded an astracode transfer function with an accuracy of about 2 c the transfer function was used to reconstruct middle pliocene 3 5 3 0 ma shallow marine climates of the western north atlantic during the marine transgression that deposited the yorktown formation virginia and north carolina the duplin formation south and north carolina and the pinecrest beds florida middle pliocene paleowater temperatures in virginia averaged 19 c in august and 13 5 c in february about 5 c to 8 c warmer than at comparable depths off virginia today august and february water temperatures in north carolina were 23 c and 13 4 c in south carolina about 23 c and 13 5 c and in southern florida about 24 6 c and 15 4 c marine climates north of 35 n were warmer than today south of 35 n they were about the same or slightly cooler thermal gradients along the coast were generally not as steep as they are today the north atlantic transfer function can be applied to other shallow marine pliocene and pleistocene deposits of eastern north america

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

a new planktic foraminifer transfer function for estimating pliocene holocene paleoceanographic conditions in the north atlantic abstract a new planktic foraminifer transfer function gsf18 related 5 north atlantic assemblages to winter and summer sea surface temperature gsf18 based on recombined and simplified core top census data preserves most environmental information and reproduces modern north atlantic conditions with approximately the same accuracy as previous transfer functions but can be more readily applied to faunal samples ranging in age from pliocene to holocene transfer function gsf18 has been applied to faunal data from deep sea drilling project hole 552a to produce a 2 5 m y sea surface temperature sst time series estimates show several periods between 2 3 and 4 6 ma during which mean sst s were both several degrees warmer and several degrees cooler than modern conditions between 2 9 and 4 0 ma sst was generally warmer than modern except for a 250 k y interval centered at 3 3 ma maximum sst with respect to modern conditions occurred after the cool interval near 3 1 ma when sst was approximately 3 6 c warmer than present conditions comparison of sst estimates with stable isotope data suggest that after peak warming at 3 1 ma there was an overall surface water cooling with concomitant build up of global ice volume culminating in northern hemisphere glaciation this event is also indicated by the presence of ice rafted detritus in 552a sediments at about 2 45 ma

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

contrasting glacial interglacial regimes in the western arctic ocean as exemplified by a sedimentary record from the mendeleev ridge distinct cyclicity in lithology and microfaunal distribution in sediment cores from the mendeleev ridge in the western arctic ocean water depths ca 1 5 km reflects contrasting glacial interglacial sedimentary patterns we conclude that during major glaciations extremely thick pack ice or ice shelves covered the western arctic ocean and its circulation was restricted in comparison with interglacial modern type conditions glacier collapse events are marked in sediment cores by increased contents of ice rafted debris notably by spikes of detrital carbonates and iron oxide grains from the canadian arctic archipelago composition of foraminiferal calcite n 18 o and n 13 c also shows strong cyclicity indicating changes in freshwater balance and or ventilation rates of the arctic ocean light stable isotopic spikes characterize deglacial events such as the last deglaciation at ca 12 14 c kyr bp the prolonged period with low n 18 o and n 13 c values and elevated contents of iron oxide grains from the canadian archipelago in the lower part of the mendeleev ridge record is interpreted to signify the pooling of freshwater in the amerasia basin possibly in relation to an extended glaciation in arctic north america unique benthic foraminiferal events provide a means for an independent stratigraphic correlation of sedimentary records from the mendeleev ridge and other mid depth locations throughout the arctic ocean such as the northwind and lomonosov ridges this correlation demonstrates the disparity of existing age models and underscores the need to establish a definitive chronostratigraphy for arctic ocean sediments 2003 elsevier b v all rights reserved

on the importance of the heterogeneity assumption in the characterization of reservoir geomechanical properties the geomechanical analysis of a highly compartmentalized reservoir is performed to simulate the seafloor subsidence due to gas production the available observations over the hydrocarbon reservoir consist of bathymetric surveys carried out before and at the end of a 10 yr production life the main goal is the calibration of the reservoir compressibility cm that is the main geomechanical parameter controlling the surface response two conceptual models are considered in one i cm varies only with the depth and the vertical effective stress heterogeneity due to lithostratigraphic variability in another ii cm varies also in the horizontal plane that is it is spatially distributed within the reservoir stratigraphic units the latter hypothesis accounts for a possible partitioning of the reservoir due to the presence of sealing faults and thrusts that suggests the idea of a block heterogeneous system with the number of reservoir blocks equal to the number of uncertain parameters the method applied here relies on an ensemble based data assimilation da algorithm i e the ensemble smoother es which incorporates the information from the bathymetric measurements into the geomechanical model response to infer and reduce the uncertainty of the parameter cm the outcome from conceptual model i indicates that da is effective in reducing the cm uncertainty however the maximum settlement still remains underestimated while the areal extent of the subsidence bowl is overestimated we demonstrate that the selection of the heterogeneous conceptual model ii allows to reproduce much better the observations thus removing a clear bias of the model structure da allows significantly reducing the cm uncertainty in the five blocks out of the seven characterized by large volume and large pressure decline conversely the assimilation of land displacements only partially constrains the prior cm uncertainty in the reservoir blocks marginally contributing to the cumulative seafloor subsidence that is blocks with low pressure

stable isotope stratigraphy sedimentation rates and salinity changes in the latest pleistocene to holocene eastern central arctic ocean a high resolution study including oxygen and carbon stable isotopes as well as carbonate and total organic carbon contents has been performed on undisturbed near surface 0 40 cm sediment sequences taken in the eastern arctic ocean during the international arctic 91 expedition based on the oxygen stable isotope records measured on neogloboquadrina pachyderma sin and ams 14c dating the upper 10 to 20 cm of the sediment sequences represent isotope stage 1 and the base of termination i 15 7 ka can be identified very well stage 1 sedimentation rates vary between 0 4 and 2 0 cm kyr in general glacial stage 2 sedimentation rates are probably lower and vary between 0 4 and 0 7 cm kyr the glacial interglacial shifts in 18o values of n pachyderma sin may reach values of 1 3 to 2 5 indicating 1 that in addition to the glacial interglacial global ice volume signal changes in surface water salinity have effected the isotope records and 2 that these salinity changes have varied laterally glacial interglacial differences in salinity were small in the lomonosov ridge area 0 0 4 and relatively high in the morris jesup rise area up to 1 4 this implies that the supply of low saline waters onto the eurasian shelves and its further transport into the central arctic ocean via the transpolar drift should have continued during the last glacial and should have significantly influenced the surface water characteristics in parts of the central arctic on the morris jesup rise on the other hand the glacial low saline water signal at that time was strongly reduced in comparison to the modern situation at the glacial interglacial stage 12 boundary a strong meltwater signal is recorded in a sharp depletion in 18o as well as 13c this central arctic ocean meltwater event can be correlated from the makarov basin through the lomonosov ridge and amundsen basin to the eastern gakkel ridge the beginning of this event is ams 14c dated at 15 7 ka i e significantly older than the major decrease in the global ice volume signal which occurs between 9 and 13 5 ka large amounts of freshwater meltwater were probably supplied from the eurasian continent due to the decay of the barents sea ice sheet causing this distinct early meltwater anomaly in the central arctic ocean the extension of a well oxygenated surface near water mass in the arctic ocean and at least seasonal open ice conditions and some increased bioproductivity were probably established at the end of termination i as indicated by the increase in 13c to modern values as well as increased carbonate i e foraminifers coccoliths ostracodes and total organic carbon contents

ii cycle compressibility from satellite measurements knowledge of ground compressibility in unloading reloading conditions is of paramount importance in several geomechanical processes but its estimate is often affected by large uncertainties especially for deep rocks satellite measurements of the land motion can help improve this information the present study investigates the ground response due to underground gas storage activities as revealed by satellite interferometric measurements in three gas fields of the po river basin italy the ground proves to behave elastically moving upwards and downwards in response to gas injection and extraction respectively the accurate calibration of a detailed geomechanical transversely isotropic finite element model allows for an indirect estimate of the vertical ground compressibility in unloading reloading conditions which proves consistent with the results already available from the same basin assuming a hypo plastic constitutive model for the compressibility in virgin loading conditions the ratio betwee

quaternary sea ice history in the arctic ocean based on a new ostracode sea ice proxy paleo sea ice history in the arctic ocean was reconstructed using the sea ice dwelling ostracode acetabulastoma arcticum from late quaternary sediments from the mendeleyev lomonosov and gakkel ridges the morris jesup rise and the yermak plateau results suggest intermittently high levels of perennial sea ice in the central arctic ocean during marine isotope stage mis 3 25 45 ka minimal sea ice during the last deglacial 16 11 ka and early holocene thermal maximum 11 5 ka and increasing sea ice during the mid to late holocene 5 0 ka sediment core records from the iceland and rockall plateaus show that perennial sea ice existed in these regions only during glacial intervals mis 2 4 and 6 these results show that sea ice exhibits complex temporal and spatial variability during different climatic regimes and that the development of modern perennial sea ice may be a relatively recent phenomenon

a 600 ka arctic sea ice record from mendeleev ridge based on ostracodes arctic paleoceanography and sea ice history were reconstructed from epipelagic and benthic ostracodes from a sediment core hly0503 06jpc 800 m water depth located on the mendeleev ridge western arctic ocean the calcareous microfaunal record ostracodes and foraminifers covers several glacial interglacial cycles back to estimated marine isotope stage 13 mis 13 500 ka with an average sedimentation rate of 0 5 cm ka for most of the stratigraphy mis 5 13 results based on ostracode assemblages and an unusual planktic foraminiferal assemblage in mis 11 dominated by a temperate water species turborotalita egelida show that extreme interglacial warmth high surface ocean productivity and possibly open ocean convection characterized mis 11 and mis 13 400 and 500 ka respectively a major shift in western arctic ocean environments toward perennial sea ice occurred after mis 11 based on the distribution of an ice dwelling ostracode acetabulastoma arcticum spectral analyses of the ostracode assemblages indicate sea ice and mid depth ocean circulation in western arctic ocean varied primarily at precessional 22 ka and obliquity 40 ka frequencies

late neogene climate evolution of the central arctic ocean abstract because no sediment of post eocene to late miocene or pliocene age has been recovered from the central arctic ocean oceanographic conditions during the middle cenozoic are unknown the oldest late cenozoic sediment is glacial marine and contains agglutinated foraminifera a few calcareous organisms are present in the oldest late cenozoic sediment with an age of 2 4 ma but at approximately the time as deposition of lithostratigraphic unit f sometime between 2 0 and 1 5 ma there was an abrupt and dramatic increase in calcareous species diversity and abundance in the central arctic ocean many of the newly introduced species are atlantic in origin preliminary evidence suggests that the introduction of a moderately large and diverse calcareous fauna at this time corresponds to the lowering of the arctic ocean ccd level and this may be explained by increased circulation with the northern greenland sea details of the change in threshold values in the fram strait required for the introduction of relatively warmer and carbonate rich water into the central arctic ocean are unknown there is evidence that spreading rates along the north atlantic nansen ridge system increased during the pleistocene and this may have permitted increased circulation between the north atlantic and the central arctic ocean this important change in arctic ocean circulation corresponds to increased pleistocene seasonality in the northern hemisphere

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions

a new bipolar ice core record of volcanism from wais divide and neem and implications for climate forcing of the last 2000 years volcanism is a natural climate forcing causing short term variations in temperatures histories of volcanic eruptions are needed to quantify their role in climate variability and assess human impacts we present two new seasonally resolved annually dated non sea salt sulfur records from polar ice cores wais divide wdc06a from west antarctica spanning 408 b c e to 2003 c e and neem neem 2011 s1 from greenland spanning 78 to 1997 c e both analyzed using high resolution continuous flow analysis coupled to two mass spectrometers the high dating accuracy allowed placing the large bi hemispheric deposition event ascribed to the eruption of kuwae in vanuatu previously thought to be 1452 1453 c e and used as a tie point in ice core dating into the year 1458 1459 c e this new age is consistent with an independent ice core timescale from law dome and explains an apparent delayed response in tree rings to this volcanic event a second volcanic event is detected in 1453 c e in both ice cores we show for the first time ice core signals in greenland and antarctica from the strong eruption of taupo in new zealand in 232 c e in total 133 volcanic events were extracted from wdc06a and 138 from neem 2011 s1 with 50 ice core signals predominantly from tropical source volcanoes identified simultaneously in both records we assess the effect of large bipolar events on temperature sensitive tree ring proxies these two new volcanic records synchronized with available ice core records to account for spatial variability in sulfate deposition provide a basis for improving existing time series of volcanic forcing

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

pliocene palaeotemperature reconstruction for the southern north sea based on ostracoda abstract the development of a large northeastern atlantic shelf ostracod database has confirmed that an intrinsic relationship exists between watermass temperature and the spatial latitudinal distribution of benthonic shelf ostracoda a second pliocene ostracod database using assemblages from four boreholes in the netherlands and a number of localities from the east anglian neogene succession has also been constructed a quantitative method of modern analogues and the squared chord distance dissimilarity coefficient has been employed as a means of calculating the level of similarity between recent and neogene assemblages and therefore to aid in the reconstruction of palaeotemperatures in the southern north sea basin during the pliocene the results in the form of contoured dissimilarity values indicate the presence of at least seven palaeoceanographical climatic phases between ca 5 2 and 1 6 ma bp an early pliocene cooling phase ecozone a in which the fauna is dominated by the cryophilic species palmenella limicola norman elofsonella concinna jones robertsonites tuberculatus sars neomonoceratina tsurugasakensis tabuki and acanthocythereis dunelmensis norman supervenes a period of stable subtropical conditions in the miocene a mid pliocene warming phase ecozone b which has been documented throughout the north atlantic can be recognized in the faunal composition of the sublittoral ostracod assemblages of both the netherlands and east anglia a hiatus between the coralline and waltonian crags is thought to be associated with a deterioration in climatic conditions recent analogues to the netherlands faunas of ecozone c first phase late pliocene cooling ca 2 9 ma bp indicate a decrease of approximately 5 6 c in mean summer surface temperatures a return to elevated temperatures of a mauritanian aspect can be seen in the fauna of the fa2 zone and waltonian crag this amelioration of climate occurred prior to the praetiglian cold phase second phase late pliocene cooling ca 2 4 ma bp which again saw the reintroduction of cryophilic species including baffinicythere howei hazel fimarchinella logani brady crosskey and robertson and hemicythere emarginata sars into the southern north sea during the newbournian and butleyan stages the final phase of the latest pliocene third phase late pliocene cooling is only documented in the ostracod fauna of the norwich crag evidence in the covariance of loxoconchidae and norwegian provincial cryophilic species indicates that the polar front may have been as much as 2000 km further south during the deposition of the chillesford sand member norwich crag fm ca 2 0 1 6 ma bp