oxygen and carbon isotope record of east pacific core v19 30 implications for the formation of deep water in the late pleistocene north atlantic abstract a detailed oxygen and carbon isotope record has been obtained from benthic foraminifera in core v19 30 from the carnegie ridge on the south side of the panama basin expressing these records and the oxygen and carbon isotope records previously published for atlantic core m 12392 on a common timescale it is apparent that the oxygen isotope records are very similar but that the carbon isotope records are quite different by obtaining the carbon isotope gradient between the two sites as a function of time we show that the production of north atlantic deep water has varied over a wide range during the late pleistocene and that the pattern of variation is not simply related to the well known oxygen isotope record although the two oxygen isotope records are very similar changes in the interoceanic gradient are detectable and support the hypothesis that in the glacial mode the north atlantic was colder and less oxygenated than it is today shackleton s 1 1977 interpretation whereby the carbon isotope record from the atlantic core reflects changes in the terrestrial biomass is an over simplification however the record from the pacific core v19 30 probably can be explained in these terms since it probably approximates the carbon isotope record of global mean oceanic dissolved co 2

quaternary sediments and environments on the continental shelf off northern norway abstract based on lithologic palaeontologic and chronostratigraphic investigations of close to 200 gravity cores from troughs deep banks and shallow banks the following late quaternary environment can be outlined in the weichselian deposition of basal tills was followed by deposition of laminated clay in a sea ice environment later a pebbly pelite was deposited in the troughs at the same time as the banks were iceberg ploughed then 13 000 yrs b p a period with incipient winnowing occurred on the deep banks and deposition of sandy pelite took place in the troughs the holocene commenced with a marked environmental change due to intrusion of atlantic water the fauna changed from arctic to boreal high energy winnowing forming a lag deposit took place on the banks and high accumulation rates in the troughs occurred due to the winnowing and sediment influx from the downwasting continental icesheet during the later part of the holocene the winnowing diminished on the deeper banks on the shallow banks and on the shelf break it still prevails and in the troughs calcareous sandy mud is being deposited the surface sediments comprise three main facies bouldery and pebbly sand sand and sandy mud whose distribution mainly depends on the prevailing bottom current regime the composition of the older quaternary sediments is demonstrated by some selected seismic profiles

central arctic surface ocean environment during the past 80 000 years stable oxygen and carbon isotope and sedimentological paleontological investigations supported by accelerator mass spectrometry 14 c datings were carried out on cores from north of 85 degrees n in the eastern central arctic ocean significant changes in accumulation rates provenance of ice rafted debris ird and planktic productivity over the past 80 000 years are documented during peak glacials i e oxygen isotope stages 4 and 2 the arctic ocean was covered by sea ice with decreased seasonal variation limiting planktic productivity and bulk sedimentation rates in early stage 3 and during termination i major deglaciations of the circum arctic regions caused lowered salinities and poor oxygenation of central arctic surface waters a meltwater spike and an associated ird peak dated to similar to 14 12 14 c ka can be traced over the southern eurasian basin of the arctic ocean this event was associated with the early and rapid deglaciation of the marine based barents sea ice sheet a separate termination ib meltwater event is most conspicuous in the central arctic and is associated with characteristic dolomitic carbonate ird this lithology suggests an origin of glacial ice from northern canada and northern greenland where lower paleozoic platform carbonates crop extensively out

rapid climatic shifts during isotope stages 2 4 in the polar north atlantic sediment cores from the polar north atlantic provide evidence of six periods of sea ice breakup during isotope stages 4 3 and 2 probably caused by inflow of north atlantic surface water into the polar north atlantic these periods are characterized by having a high number of foraminifera g they last from 2000 to 10000 yr and constitute 50 of the total time span these periods of sea ice breakup correlate temporarily to the heinrich events and the early temperature maximum in the bond cycles of the north atlantic and greenland ice record our hypothesis is that massive iceberg discharges that flooded the north atlantic during each heinrich event probably triggered an oceanographic regime that gave a much more vigorous surface circulation pattern in the polar north atlantic which contributed to the breakup of the sea ice cover open water conditions in the polar north atlantic are inversely related to terrestrial interstadials of coastal norway suggesting ice sheet starvation during the cold periods and ice sheet growth when an open water surface circulation existed in the polar north atlantic our data document synchronous variations on a october 1900 yr time scale between arctic oceanic climate northern hemisphere ice sheet dynamics and ocean atmosphere temperature changes

parent brine of the castile evaporites upper permian texas and new mexico abstract the upper permian lower ochoan castile formation is a major evaporite sequence 10 000 km3 of calcite anhydrite and halite in west texas and southeastern new mexico traditionally the castile brine has been considered to have been derived from seawater this tradition has recently been challenged by two versions of the closed basin drawdown model they call for deposition from a mixed brine in part marine and in large part nonmarine they propose drawdown of as much as 500 m to form a major sink for ground water issuing from the surrounding capitan reef complex a large fraction of the solute in the brine body is inferred to have been recycled from older permian evaporites on the surrounding shelf strontium isotope analyses show no evidence that meteoric ground water was contributed to the castile brine from a stratigraphic geographic and lithologic array of 65 samples of anhydrite gypsum and calcite 59 have an 87sr 86sr ratio of 0 706923 sw of 225 0 a ratio that is the same as that of strontium in early ochoan ocean water if considerable 15 influx of meteoric water had occurred enough continental strontium would have been introduced to have resulted in higher ratios low bromide values 20 40 ppm in castile halite which have been used to argue for meteoric influx and for recycled salt probably resulted from diagenesis during shallow burial by halite centimeter size bottom grown crystals of gypsum were altered to nodular anhydrite the rising water of dehydration caused the halite to recrystallize during the recrystallization some bromide was expelled despite the large volume of water that evaporated annually from its surface 52 km3 yr assuming an evaporation rate of 2 m yr the castile brine body never completely desiccated the surrounding shelf was flat hot and generally dry it probably could not have supplied a significant volume of meteoric spring water to the basin over tens of thousands of years more likely during the entire history of the evaporite sequence influx was dominantly marine marine ground water flowed through the capitan formation into the evaporite basin along its southern and possibly western margin probably with a rate of flow that was usually fast enough to prevent major drawdown of the brine surface

foraminiferal stratigraphy and environment of late weichselian deposits on the continental shelf off troms northern norway abstract based on the analysis of 8 selected gravity cores from the upper sediment layers of andfjorden and malangsdjupet off northern norway six late weichselian foraminiferal assemblage zones are defined the two oldest assemblage zones 8 and 7 are found in basal tills and contain mixed faunas reworked and deposited by glaciers which reached the shelf edge during the early late weichselian during the earliest phase of the deglaciation of the continental shelf a sparse fauna characterized by buccella frigida zone 6 was deposited zone 5 is dominated by cassidulina laevigata and a fairly high content of planktic foraminifera indicating periods of ice free normal marine surface waters during a glacial advance between 14 000 and 13 000 b p the fauna zone 4 was dominated by elphidium excavatum this fauna reflects near glacial conditions characterized by unstable bottom water conditions the last c 500 years of this period suffered from oxygen depleted bottom waters zone 3 formed between 13 000 and 10 000 b p comprises several species e g cassidulina reniforme nonion barleeanum n labradoricum and cibicides lobatulus during the first 2000 years of this period the fauna reflects a climatic amelioration e g an increase in temperature salinity and current activity probably due to intrusion of atlantic water during the younger dryas zone 3 reflects a climatic deterioration

late weichselian submarine debris flow deposits on the bear island trough mouth fan sedimentary processes on the bear island trough mouth fan during the last glacial were studied using high resolution reflection seismics and gravity cores the fan succession is dominated by large debris flow deposits of up to 24 km in width and 50 m thick debris lobes can be followed over 100 km downslope and the largest cover an area of 1880 km2 the large debris flows were generated when the barents sea ice sheet reached the shelf break glacigenic sediments transported to the grounding line were temporarily stored on the upper slope due to the high sedimentation rate the sediments were unstable and earthquakes oversteepening and or build up of excess pore pressure triggered sediment release generating large debris flows sediments were also eroded and incorporated during the downslope flow debris flows were the most important sediment distributing process due to the relatively high shear strength low flow mobility of the glacigenic diamicton and the low fan gradient the weichselian evolution of the fan was characterized by a relatively low sedimentation rate during the early and mid weichselian the barents sea ice sheet might have reached the shelf break twice during the late weichselian on average one large debris flow comprising 18 km3 of sediments was released between every 35 to 75 years during the last glacial maximum

u pb dates of paleosols constraints on late paleozoic cycle durations and boundary ages u pb ages of paleosol samples from cyclothemic sections in the sacramento mountains of new mexico and the permian basin of west texas bracket the pennsylvanian permian and carboniferous permian boundaries linear interpolation and extrapolation to boundaries are accomplished by using cyclothems as periodic subdivisions the carboniferous permian boundary is 301 2 ma 2 the pennsylvanian permian boundary is 302 2 4 2 and the missourian virgilian boundary is 307 3 ma 2 these ages are within the uncertainties of recent estimates for the boundaries but are significantly more precise the average cycle duration for this upper pennsylvanian and lower permian interval is 143 64 ka 2 within the uncertainty of the 100 k y cycle that dominated pleistocene sea level history this new estimate which is much shorter than those published previously suggests that the pennsylvanian and early permian cyclothems may have been driven in a manner similar to that which caused glacio eustatic cycles of the pleistocene

timing of the permian triassic biotic crisis implications from new zircon u pb age data and their limitations abstract the most profound biotic crisis in the earth s history causing the near extinction of both terrestrial and marine life occurred at the end of the permian period about 253 myr ago and marks the paleozoic mesozoic era boundary the cause of this event is still a matter of vigorous debate with both brief and catastrophic as well as gradual mechanisms having been proposed similar to a recent landmark study this study uses the u pb method on zircons from the uppermost permian lowermost triassic ash fall deposits at meishan zhejiang province se china in order to examine time and rate constraints for these events the results of both this study and previous work show that for these ash layers the effects of pb loss are combined with varying amounts and sources of inheritance resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases though the effects of pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid as opposed to commonly applied air abrasion prior to analysis the presence within a single ash layer of multiple generations of older xenocrysts in many cases only slightly older than the depositional age has made quantitative interpretation even more difficult when these combined phenomena bias individual zircon ages by less than a percent they are extremely difficult to deconvolute and if multi grain analyses are used can become impossible to recognize because of the resulting age averaging monte carlo simulations using actual measurements of individual zircon crystals show that age excursions due to pb loss and xenocrystic contamination for the meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi grain zircon samples are compared thus this study uses only high precision analyses of single crystals whether from our work or that of previous studies three main conclusions have emerged first our data require a significant increase in the age of the permian triassic boundary by more than 2 myr compared to the previous study which shifts the age to a value older than 253 ma second neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis third even large suites of very high quality single zircon u pb analyses for these tuffs cannot in most cases yield objective reliable and robust dates with accuracies at the sub myr level though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible the last conclusion is not an indictment of zircon u pb dating in general other rocks and other zircon populations can and do behave very differently and further technical advances will likely improve our ability to prepare grains or sub grains of adequately enhanced quality for analysis consequently the results of the present study strongly suggest that for problems requiring time scale accuracy inferences from zircon u pb dating must be based on sufficiently large suites of single crystal or crystal domain high precision analyses

the last deglaciation event in the eastern central arctic ocean oxygen isotope records of cores from the central arctic ocean yield evidence for a major influx of meltwater at the beginning of the last deglaciation 15 7 thousand years ago 16 650 calendar years b c the almost parallel trends of the isotope records from the arctic ocean the fram strait and the east greenland continental margin suggest contemporaneous variations of the eurasian arctic and greenland laurentide ice sheets or increased export of low saline waters from the arctic within the east greenland current during the last deglaciation on the basis of isotope and carbon data the modern surface and deep water characteristics and seasonally open ice conditions with increased surface water productivity were established in the central arctic at the end of termination lb about 7 2 thousand years ago or 6 000 calendar years b c

impact of southeast indian ocean sea surface temperature anomalies on monsoon enso dipole variability in a coupled ocean atmosphere model recent studies show that southeast indian ocean seio ssts are a highly significant precursor of transitions of the whole monsoon el nino southern oscillation enso system during recent decades however the reasons for this specific interannual variability have not yet been identified unequivocally from the observations among these the possibility of seio sst driven variability in the monsoon enso system is investigated here by inserting positive negative seio temperature anomalies in the february s restart files of a state of the art coupled general circulation model gcm for 49 years of a control simulation for each year of the control simulation the model was then integrated for a 1 year period in fully coupled mode these experiments show that indian summer monsoon ism and tropical indian ocean dipole mode iodm events are significantly influenced by the seio temperature perturbations inserted in the mixed layer of the coupled gcm several months before a warm seio perturbation inserted in late boreal winter slowly propagates northward during the following seasons implies enhanced ism rainfall and finally triggers a negative iodm pattern during boreal fall in agreement with observations a reversed evolution is simulated for a cold seio perturbation it is shown that the life cycle of the simulated seio signal is driven by the positive wind evaporation sst coastal upwelling and wind thermocline sst feedbacks further diagnosis of the sensitivity experiments suggests that stronger ism and iodm variabilities are generated by excluding the el nino years of the control simulation or when the initial background state in the seio is warmer this finding confirms that iodm events may be triggered by multiple factors other than enso including subtropical seio sst anomalies however the enso mode does not react significantly to the seio temperature perturbation in the perturbed runs even though the simulated pacific pattern agrees with the observations during boreal fall these discrepancies with the observations may be linked to model biases in the pacific and to the too strong enso simulated by this coupled gcm these modeling evidences confirm that subtropical indian ocean sst anomalies generated by mascarene high pulses during austral summer are a significant precursor of both ism and iodm events occuring several months later

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary abstract organic rich calcite laminated with gypsum in the evaporitic non fossiliferous castile formation of the delaware basin southwest usa yields a total pb u isochron age of 251 5 2 8 ma mswd 1 3 the castile formation is almost certainly late permian based on its 87 sr 86 sr value of 0 706923 identical to the distinct minimum in the late permian sr curve in this paper we explore the potential for using u pb calcite ages to date traditionally undatable sections and show how this southern midcontinent usa far west texas and southeast new mexico deposit can be correlated to the type section in china we accept that diagenetic alteration can bias u pb results but the data set we present shows no evidence for such alteration clearly with alteration the age we present would represent a minimum age for the castile formation if the age actually dates the castile formation then it requires the permian triassic boundary to be younger than 251 5 2 8 ma

indian ocean sea surface temperature and el nino southern oscillation a new perspective abstract here the 1976 77 climate regime shift that was accompanied by a remarkable change in the lead lag relationships between indian ocean sea surface temperature sst and el nino evolution is shown after the 1976 77 regime shift a correlation analysis suggests that southern indian ocean ssts observed during late boreal winter are a key precursor in predicting el nino evolution as the traditional oceanic heat content anomalies in the equatorial pacific or zonal wind anomalies over the equatorial western pacific the possible physical mechanisms underlying this highly significant statistical relationship are discussed after the 1976 77 regime shift southern indian ocean sst anomalies produced by mascarene high pulses during boreal winter trigger coupled air sea processes in the tropical eastern indian ocean during the following seasons this produces a persistent remote forcing on the pacific climate system promoting wind anomalies over the western equatorial pacific and modulating the regional ha

structure and mechanisms of the southern hemisphere summertime subtropical anticyclones abstract the three dimensional structure and dynamics of the climatological mean summertime subtropical anticyclones in the southern hemisphere sh are investigated as in the northern hemisphere nh each of the surface subtropical anticyclones over the south pacific south atlantic and south indian oceans is accompanied by a meridional vorticity dipole aloft exhibiting barotropic and baroclinic structures in its poleward and equatorward portions respectively in a manner that is dynamically consistent with the observed midtropospheric subsidence their dynamics are also similar to their nh counterpart it is demonstrated through the numerical experiments presented here that each of the sh surface anticyclones observed over the relatively cool eastern oceans can be reproduced as a response to a local near surface cooling heating couplet the cooling is mainly due to radiative cooling associated with low level maritime clouds and the heating to the east is due to sensible heat flux over the dry hea

macrofaunal palaeoecology and stratigraphy in late quaternary shelf sediments off northern norway abstract in a late pleistocene holocene glaciomarine marine sequence a minimum of 115 taxa macrofossils and trace fossils are recognized on the basis of 690 samples from gravity cores from andfjorden nine and malangsdjupet one the biostratigraphy is proposed on the basis of reconstructions of autochthonous macrofaunal assemblages a total of seven zones are defined five in the pleistocene and two in the holocene the ages of which are estimated by radiocarbon datings in ascending order the zones are mixed assemblage zone barren interzone arctinula greenlandica assemblage zone before 14 000 yr b p yoldiella intermedia assemblage zone 14 000 13 000 yr b p bathyarca glacialis assemblage zozne 13 000 yr b p bathyarca glacialis kelliella miliaris interval zone 10 000 ca 7800 yr b p and kelliella miliaris assemblage zone ca 7800 present the bathyarca glacialis zone is divided into three faunules i 13 000 12 000 yr b p ii 12 200 11 100 yr b p and iii 11 100 10 000 yr b p the palaeoecology of the faunal succession is elucidated by means of the sample frequency method two major environmental events have influenced the faunal history the first was the onset of the deglaciation of the thoughs the second the intrusion of the norwegian current bringing warm saline atlantic water into the troughs at 10 000 yr b p the pleistocene fossils demonstrate an arctic macrofaunal succession from a low order stage to a high order equilibrium stage that is in principle identical to that of a modern faunal development in fjords following a disturbance causing anoxia an estimated polychaete mollusc ratio together with changes in sediment influx depositional rates and grain size of substrate indicate the presence of different energy regimes where the inner and outer reaches of andfjorden are compared about 10 000 yr b p a major faunal change took place the previous arctic fauna was replaced by a boreal fauna which developed into the modern fauna the most important factor causing the replacement and renewed faunal succession were probably the rise in temperature and salinity as well as an increase in nutrient supply brought about by the intrusion of the norwegian current a comparison with shallower shelf areas indicates a somewhat different faunal composition in the pleistocene brought about by different depositional environments however a similar major faunal change took place at 10 000 yr b p and there are fewer discrepancies among the holocene faunas regional comparison indicates that some of the phases in the development of the fauna probably are rather local while other have a more regional nature

directly dating geologic events u pb dating of carbonates 1 carbonates are ubiquitous forming in a variety of settings including caves soils the oceans during burial from hydrothermal fluids and along faults u pb dating of carbonates is applicable to almost the entire geologic time scale with results from pleistocene speleothems showing great promise for dating records 1 ma old here we review studies of u pb dating of carbonates from a range of depositional and diagenetic environments and consider published results with regard to stratigraphic associations and the behavior of u and pb in various fluids we detail the steps required to select suitable samples summarize current laboratory techniques and provide directions for improvement of analytical protocols the u pb dating of carbonates has tremendous potential for dating events of geologic interest and is virtually untapped

subtropical dipole modes simulated in a coupled general circulation model the growth and decay mechanisms of subtropical dipole modes in the southern indian and south atlantic oceans and their impacts on southern african rainfall are investigated using results from a coupled general circulationmodeloriginallydevelopedforpredictingtropicalclimatevariations thesecond most dominant mode of interannual sea surface temperature sst variations in the southern indian south atlantic ocean represents a northeast southwest oriented dipole now called subtropical dipole mode the positive negative sst interannualanomalypole startsto grow in australspring and reachesits peakin february in austral late spring the suppressed enhanced latent heat flux loss associated with the variations in the subtropical high causes a thinner thicker than normal mixed layer thickness that in turn enhances reduces the warming of the mixed layer by the climatological shortwave radiation the positive negative pole gradually decays in austral fall because the mixed layercooling by the entrainmentis enhanced reduced mostlyowing to the larger smaller temperature difference between the mixed layer and the entrained water the increased decreased latent heat loss due to the warmer colder sst also contributes to the decay of the positive negative pole although furtherverification using longerobservational data is required the present coupled model suggests that the south atlantic subtropical dipole may play a more important role in rainfall variations over the southern african region than the indian ocean subtropical dipole

subtropical sst dipole events in the southern indian ocean sea surface temperature sst anomalies in the subtropical southern indian ocean show interannual dipole events that are seasonally phase locked to the austral summer a positive phase of the event is characterized by cold sst anomalies in the eastern part i e off australia and warm sst anomalies in the southwestern part south of madagascar such an event is found to produce above normal rainfall over many regions in south central africa the cooling of sst in the eastern part is mainly caused by the enhanced evaporation this is associated with stronger winds along the eastern edge of the subtropical high which is strengthened and shifted slightly to the south during the event on the other hand relative decrease in the seasonal latent heat loss due to reduced evaporation dominates the warming in the southwestern part evolution of such subtropical dipole events shows quite a contrast to that of the tropical dipole events discovered recently in the indian ocean

the impact of diagenesis on high precision upb dating of ancient carbonates an example from the late permian of new mexico we have applied upb trace element and sr isotopic analyses to subsamples of a single specimen of the capitan formation from the permian reef complex of new mexico with the goal of calibrating the late permian time scale and understanding the factors that set and later alter the initial u pb ratio and pb isotopic composition of the limestone the data indicate a limestone upb isochron age of 249 8 4 7 ma 2 and a pbpb age of 249 18 ma in addition with values 238u 204pb ranging up to 4200 among the highest ever recorded for a limestone we also obtain precise single sample 206pb 238u 207pb 235u and 207pb 206pb ages indicating averages of 250 2 3 2 ma 250 0 2 8 ma and 256 3 3 5 ma respectively comparison of the average pb u age of 250 3 ma for the latest guadalupian with published radiometric constraints for the late permian suggests preservation of essentially the depositional age trace element and sr isotopic analyses highlight four samples that preserve a chemical signature expected for primary marine aragonite including high sr 3000 g g high u 2900 ng g low initial pb 26 g g and 87sr 86sr 0 7073 as well as the lower u and higher pb mg and fe expected for a diagenetically altered carbonate these data clearly delineate the diagenetic alteration of the limestone and allow us to demonstrate the critical importance of diagenesis in controlling the spread in values primarily through the expulsion of u but with some incorporation of pb the high are simply a function of preservation of original carbonate chemistry and not of u scavenging by fe oxyhydroxides or phosphates although it has long been suspected that limestone upb and pbpb isochron ages reflect the timing of early diagenesis as opposed to a strictly depositional age this is the first study in which this is conclusively demonstrated to be the case the upb data also suggest a late stage neogene alteration that disturbed the system mainly via the redistribution of u intriguingly the four samples that best retain their primary marine aragonitic geochemistry also best maintained a closed upb system most of the subsamples with comparably high values but clearly altered trace element compositions showed upb systematics indicating late disturbance unfortunately it is not yet possible to determine which processes are responsible for this late stage alteration and it is unclear exactly how to avoid such alteration in future work

stable oxygen and carbon isotopes in planktic foraminifers from arctic ocean surface sediments reflection of the low salinity surface water layer planktic foraminifers neogloboquadrina pachyderma sin from 87 eastern and central arctic ocean surface sediment samples were analyzed for stable oxygen and carbon isotope composition additional results from 52 stations were taken from the literature the lateral distribution of 18o full size image 33 atlantic waters entering the arctic ocean through the fram strait 18o values decrease both to the barents shelf and to the north pole in accordance with the decreasing salinities of the halocline waters in the nansen basin a strong n s 18o gradient is in contrast with a relatively low salinity change and suggests contributions from different freshwater sources i e salinity reduction from sea ice meltwater in the south and from light isotope waters meteoric precipitation and river runoff in the northern part of the basin north of the gakkel ridge 18o and salinity gradients are in good accordance and suggest less influence of sea ice melting processes the 13c full size image 1 k values of n pachyderma sin from arctic ocean surface sediment samples are generally high 0 75 0 95 lower values in the southern eurasian basin appear to be related to the intrusion of atlantic waters the high 13c values are evidence for well ventilated surface waters because the perennial arctic sea ice cover largely prevents atmosphere ocean gas exchange ventilation on the seasonally open shelves must be of major importance lack of 13c gradients along the main routes of the ice drift from the siberian shelves to the fram strait suggests that primary production i e co2 consumption does probably not change the co2 budget of the arctic ocean significantly

recent calcium carbonate dissolution in the barents sea paleoceanographic applications abstract studies of benthic foraminifera in surface sediments of the arctic epicontinental barents sea show several indications of calcium carbonate dissolution low values of calcium carbonate correspond to low ratios of calcareous agglutinating foraminifera planktic benthic foraminifera high ratios of living dead foraminifera corroded calcareous foraminifera and high numbers of exposed organic linings of foraminifera dissolution increases eastwards and northwards in the study area we suggest that the dissolution is caused by the presence of dense cold saline and co 2 rich bottom water which is linked to sea ice production and the position of the oceanic polar front we also think calcium carbonate dissolution in this area indicates a sink for atmospheric co 2

concurrent u pb age and seawater 87sr 86sr value of a marine cement the purpose of this contribution is to show that it is possible to obtain accurate depositional u pb ages and original marine 87sr 86sr values from the same sample of marine cement altered marine aragonite cements from algal mounds of the late carboniferous bursum stage laborcita formation yield a u pb age of 300 2 3 8 ma consistent with the existing chronostratigraphic framework we use fluid rock interaction models to extrapolate to original seawater 87sr 86sr values based on sr isotope and trace element analyses of multiple petrographically identified components that should represent mixes of primary and diagenetic fluids such modeling provides a range of 0 70807 0 70820 for the 87sr 86sr value of the marine end member these data combined with a 87sr 86sr value of 0 70849 0 00001 for unaltered aragonite from algal plates and bivalves in the underlying holder formation show a decreasing trend in 87sr 86sr toward the end of the carboniferous whereas the range in 87sr 86sr values from the laborcita formation is consistent with existing sr curves the 87sr 86sr values of the aragonite are appreciably higher than these curves at least 0 0001 the aragonite from the holder formation has greater than 6000 ppm sr and thus these components should reflect the original marine value data from marine cements and biogenic aragonite from other sections are necessary to evaluate whether the 87sr 86sr values from the sacramento mountains truly record the global value

relationship of uranium to petrography of caliche paleosols with application to precisely dating the time of sedimentation abstract we use petrography combined with fission track mapping to evaluate qualitatively the phases that concentrate uranium in caliche paleosols from late paleozoic cyclothems of texas and new mexico we also discuss geochemical analyses of u and pb concentrations and pb isotopic compositions uranium concentrations in brown caliche calcite range from 1 to 9 ppm lead concentrations in the same calcites range from 0 5 to 1 ppm lead isotope compositions range from common no apparent radiogenic component to lead with a substantial radiogenic component caliches with brown calcite most likely developed near the vadose phreatic interface often a redox boundary where organic material and uranium is expected to be concentrated in contrast uranium concentrations in light colored caliche nodules from the vadose zone have uranium concentrations that are 1 ppm or less fifteen of forty five samples from this study have a range in u pb that would permit precise dating of the rocks but only the data from three give precise ages some of the samples have hematite which has high concentrations of u and pb for one of the precisely dated samples the two sigma uncertainty was improved from 10 to 2 6 ma by avoiding hematite when sampling

on the relationship between indian ocean sea surface temperature and the transition from el nino to la nina the relationship between indian ocean sea surface temperature and the transition of el nino events into either la nina or el nino southern oscillation neutral conditions is examined in both observations and the retrospective ensemble hindcasts of the national center for environmental prediction climate forecast system the southern indian ocean is shown to demonstrate a particularly robust and consistent relationship with the evolution of these transitions these associations are described and a physical mechanism involving air sea interaction in the indian and western pacific oceans is proposed observations suggest that easterly surface wind anomalies in the western pacific ocean are associated with the emergence of la nina during boreal summer and fall here it is shown that these winds are significantly correlated to southern indian ocean sea surface temperature in the preceding spring that is characterized by a large scale zonal dipole of cool and warm anomalies in the southwestern and southeastern indian oceans respectively these associations are particularly pronounced for strong el nino conditions during the dissipation of which a pronounced wavetrain like atmospheric pattern accompanies sea surface temperature anomalies in the southern indian ocean together the circulation and sea surface temperature anomalies increase the meridional cross equatorial temperature gradient in the western indian ocean and mute intraseasonal variability while strengthening surface equatorial easterly winds in the indo pacific warm pool collectively these anomalies favor subsequent la nina development on the basis of these observed associations a predictive model that demonstrates skill in anticipating the nature of el nino transitions involving the southern indian ocean asian monsoon and el nino southern oscillation is proposed in the national center for environmental prediction climate forecast system the relationships described above are simulated both consistently and realistically despite model weaknesses further bolstering a key role of southern indian ocean and predictive relationship comparison of fully coupled and sea surface temperature forced simulations suggests a key role for air sea interaction in the observed associations moreover it is demonstrated that coupled simulations of el nino southern oscillation may benefit substantially from improved representation of indian ocean variability and indo pacific interaction

late glacial and holocene paleoceanography and sedimentary environments in the st anna trough eurasian arctic ocean margin based on stratigraphical analysis of twelve sediment cores from the saint anna trough we reconstruct changes in paleoceanography and sedimentary environment during the last deglaciation and the holocene detailed analysis of benthic and planktic foraminiferal fauna stable oxygen and carbon isotope analysis lithostratigraphy and radiocarbon dates are used to reconstruct the following evolution after the deglaciation of the saint anna trough 13 300 yr b p until 9500 yr b p the environment was mainly characterised by low biogenic production carbonate dissolution and deposition of proximal to distal glaciomarine sediments intervals with high abundance of the benthic foraminifer cassidulina teretis may indicate influx of atlantic water at bottom the transition into the present interglacial started at 9500 yr b p reflected by increased production of foraminifera and bivalves after 8000 yr b p there was a marked drop in planktic 18o followed by a rise in planktic foraminifera and subsequently an increase of c teretis these paleoceanographic changes reflect increased heat transport into the area and are coupled to changes in nordic seas the early holocene warming of the saint anna trough were delayed by ca 2000 years relative to the northeast nordic seas early holocene sedimentation rates were relatively high 100 cm 1000 yr declining drastically after 8000 yr b p 50 cm 1000 yr this was presumably caused by reduction in winnowing and or riverine input

the indian ocean subtropical dipole mode simulated in the cmip3 models using observation data and outputs from the twentieth century climate in coupled models 20c3m control runs of coupled general circulation models submitted to the coupled model intercomparison project phase 3 cmip3 the ability of cmip3 models to simulate the indian ocean subtropical dipole iosd and its influence on the rainfall anomaly over the southern african region is investigated many models simulate the iosd but the location and shape of the sea surface temperature anomaly vary among models this model bias is closely linked to the bias in simulating the anomalous strengthening and southward shift of the subtropical high almost all models fail to simulate the rainfall anomaly associated with the iosd owing to the inaccurate simulation of the location of sea surface temperature and sea level pressure anomalies

construction of the mississippian pennsylvanian and permian seawater 87sr86sr curve abstract the estimated path of seawater 87 sr 86 sr during the mississippian pennsylvanian and permian is based on 228 analyses the samples are largely from the southern interior of the u s a where rocks of this age are widely exposed multiple analyses from single rock units are used to define the seawater ratio for different time periods the seawater 87 sr 86 sr declines from 0 70812 sw 95 mississippian to an estimated low in the early meramecian of near 0 70755 sw 152 the value rises to near 0 70812 sw 95 in latest mississippian the ratio rises to 0 70830 sw 77 in mid pennsylvanian and decreases to near 0 70809 sw 98 during virgilian time the earliest permian value is near 0 70793 sw 114 after rising to 0 70804 sw 103 in the early leonardian the seawater 87 sr 86 sr falls sharply to reach a low of 0 70672 sw 235 in ochoan time the end of the paleozoic is estimated to be near 0 70707 sw 200 based on samples from china analysis of the paleozoic curve shape shows an alternating dominance of oceanic and continental sr contributions the extended and precipitous decline in the 87 sr 86 sr during mid permian is unmatched during the phanerozoic the contrast of the paleozoic seawater sr curve shape to that in the mesozoic and cenozoic indicates a potentially fundamental change in the balance of oceanic and continental sr contributions at the end of the permian

surface oceanographic changes in the eastern labrador sea nannofossil record of the last 31 000 years abstract calcareous nannofossils in two ams 14c dated piston cores from the eastern labrador sea yield oceanographic information of the last 31 kyr moderate nannofossil productivity and abundance of north atlantic warm water taxa in the southern labrador sea core 91 045 094p suggest cool surface ocean condition between 31 and 26 thousand years ago ka the irminger current was absent in this interval thus we attribute this cool condition to weak advection of north atlantic water from the southeast we found evidence of cold and or seasonally ice covered surface conditions between 26 and 13 ka in the southern labrador sea and between 31 and 12 6 ka in the northeastern labrador sea core 90 013 013p increase of nannofossil productivity and abundance of north atlantic taxa at about 10 7 ka in core 91 045 094p suggests that the southern labrador sea was influenced by warm north atlantic surface water the polar water of the labrador current had little or no influence on the surface ocean in this area before 9 ka the labrador current started to flow or intensify after 9 ka and became strong by 8 4 ka the northeastern labrador sea remained cold until 8 4 ka perhaps because of discharge of cold meltwater from the greenland ice sheet at this time productivity increased sharply and the assemblage of nannofossils changed these suggest a significant improvement in surface ocean conditions and the establishment of the warm irminger current which marked the onset of the modern circulation pattern characterized by warm west greenland current and strong labrador current

subtropical indian ocean sst dipole events and southern african rainfall an atmospheric general circulation model agcm is used to examine how the regional atmospheric circulation and rainfall over southern africa respond to a recently observed dipole in subtropical sea surface temperature sst over the south indian ocean observations suggest that when sst is warm to the south of madagascar and cool off western australia increased summer rains occur over large areas of southeastern africa the model results suggest that this sst pattern leads to increased rainfall via enhanced convergence of moister than average air over the region increased evaporation occurs over the warm pole in the south west indian ocean and this moist air is advected towards mozambique and eastern south africa as a result of the low pressure anomaly generated over this pole which strengthens the onshore flow

synchrony and causal relations between permian triassic boundary crises and siberian flood volcanism the permian triassic boundary records the most severe mass extinctions in earth9s history siberian flood volcanism the most profuse known such subaerial event produced 2 million to 3 million cubic kilometers of volcanic ejecta in approximately 1 million years or less analysis of 40 ar 39 ar data from two tuffs in southern china yielded a date of 250 0 0 2 million years ago for the permian triassic boundary which is comparable to the inception of main stage siberian flood volcanism at 250 0 0 3 million years ago volcanogenic sulfate aerosols and the dynamic effects of the siberian plume likely contributed to environmental extrema that led to the mass extinctions

late quaternary changes in surface water and deep water masses of the nordic seas and north eastern north atlantic a review quantitative and semiquantitative proxy data based on more than 200 core top samples and 100 deep sea cores lead to important new insights about late quaternary changes in paleo oceanography climate and microfaunal habitats in the north eastern north atlantic and nordic seas insights resulting from a detailed investigation by the kiel research project sfb 313 132 summarized in this paper planktonic foraminifera species provide reliable tracers of past sea surface temperatures and currents the genus beella in particular was found to trace subtropical water masses up to the far north benthic foraminifera species served as sensors of bottom currents and local flux rates of organic matter new orders of time resolution are reached via stable isotope stratigraphy and accelerator mass spectrometry carbon 14 dating allowing the identification of meltwater events lasting a few hundred years and shorter a time range where however the yet unquantified role of bioturbation presents a growing problem based on this high resolution stratigraphy a number of time slices synoptic time intervals are defined to reconstruct the incursion of atlantic water masses to map paleocurrent patterns within the nordic seas and the north eastern north atlantic and to test alternative circulation models for example for the last glacial maximum lgm and various meltwater episodes these are clearly coeval with dansgaard oeschger events found in greenland ice cores with the actual cause of the flickering climate as yet unknown likewise there is ongoing controversy about the extent of past sea ice cover and about possible changes from the present anti estuarine to estuarine mode of deep water exchange between the north atlantic and the nordic seas during the lgm south of iceland however the history of deep water renewal over the last glacial cycle covering the last 30000 years was largely deciphered

postglacial emergence of western franz josef land russian and retreat of the barents sea ice sheet uncertainty remains on the timing and extent of late weichselian glaciers over the qsr barents and kara sea shelves franz josef land russia is a critical area for deciphering the record of glacier fluctuations and postglacial relative sea level change coastal forelands on the archipelago are covered by a well preserved raised beach sequence containing abundant and pristine driftwood whalebone and shell 4c dating of these materials provides site specific emergence records for the archipelago and some of the oldest ages on deglaciation of 10 400 bp three apparent still stands in emergence are inferred from morphology of the raised beach sequence and 4c dating between 9900 and 6200 bp and at ca 5500 bp and 3500 bp the earliest sea level arrest after formation of the marine limit reflects a balance between glacio isostasy and eustasy concomitant with the final phase of global sea level rise the latter two sea level arrests during the middle to late holocene are less pronounced and may indicate increased height of the ocean surface with greater storminess and extended open water conditions raised beaches at 1 2 m a s l and j4c dated at 1000 to 2000 bp give contemporary emergence rates of 1 to 2 mm year the low current rates of emergence on franz josef land are similar to areas in fennoscandinavia that sustained modest late weichselian glacier loads 1500 m within a few 100s of km of the inferred ice sheet margin the pattern of postglacial emergence and strandline tilts indicates that past glacier loads were greater over the adjacent barents sea than franz josef land marine and terrestrial records from franz josef land place retreat of glaciers from coastal areas by 10 400 bp whereas the adjacent franz victoria trough was deglaciated by 13 000 bp retreat of the barents sea ice sheet was probably underway by 13 500 bp coincident with rising global sea level and elevated summer insolation we infer that iceberg calving through the deep troughs bordering the barents sea particularly with rapidly rising sea level ca 12 000 bp was an important process controlling the demise of the barents sea ice sheet copyright 1996 elsevier science ltd

u pb calcite age of the late permian castile formation delaware basin a constraint on the age of the permian triassic boundary reply to a comment by ian metcalfe