chemical evolution of magmas in the proterozoic terrane of the st francois mountains southeastern missouri 1 field petrographic and major element data major element chemical data for plutonic and volcanic rocks of the eastern st francois mountains indicates that ring plutons of the butler hill caldera are low silica granites and chemically distinct from the high silica butler hill granite and grassy mountain ignimbrite additionally the ring plutons silvermine stono knoblick and slabtown granites are characterized by abundant mafic inclusions whereas these are almost completely absent in butler hill granite silvermine granite is mostly of a medium grained variety but cliffs along the st francis river expose gradations upward to a high silica fine grained cap rock least squares mixing calculations indicate that the cap rock could have formed by the fractional crystallization of plagioclase hornblende biotite magnetite and sphene all of which are liquidus phases in the medium grained silvermine granite the chemical similarity of the fine grained cap rock to butler hill granite and grassy mountain ignimbrite suggested that silvermine granite might be a sample of the parental magma from which the high silica rocks were derived least squares mixing calculations indicate that butler hill granite magma could have been derived from the composition of the average medium grained silvermine by fractional crystallization of the same liquidus phases indicated above the major element composition of grassy mountain ignimbrite can be derived from the average butler hill granite magma by fractional crystallization of plagioclase alkalic feldspar quartz biotite and magnetite all of which are liquidus phases in butler hill granite textural and chemical variations in butler hill granite from northeast to southwest suggest that the body was internally differentiated and that the present distribution of rock types is due to tilting and erosion the internal zonation of butler hill granite can be accounted for by fractional crystallization of plagioclase alkalic feldspar quartz biotite sphene and magnetite the chemical data and calculations indicate that the primary magma emplaced at the beginning of igneous activity was of silvermine type the magma crystallized fractionally so that the magma chamber became compositionally zoned with high silica magma in the upper part the top most part of this material was erupted to form grassy mountain ignimbrite during formation of the butler hill caldera subsequently more of the high silica magma was emplaced into the volcanic material in the caldera during resurgent doming after formation and resurgent doming of the butler hill caldera some of the parental magma from deeper in the chamber leaked upward into the ring fracture or into arcuate faults within the caldera forming the ring plutons the abundant mafic inclusions in the ring plutons may be earlier crystallized magma carried upward during intrusion one of the ring plutons silvermine granite apparently formed a sill like intrusion and underwent in situ differentiation a body of foliated granodiorite exposed as a giant inclusion in granite at hawn state park east of the principal exposures of the st francois mountains has the mineralogy major element chemistry and trace element chemistry to be a sample of the cumulate resulting from the processes in the magma chamber

isrm suggested methods for borehole geophysics in rock engineering in recent years many geophysical methods have been used in rock engineering for effective application of geophysics it is important to ensure that all aspects of a geophysical survey from the planning to the reporting are properly implemented to assist this in the field of rock engineering the suggested methods for geophysics have been drafted by the international society for rock mechanics commission on application of geophysics to rock engineering those for the land geophysics were already published in this journal last year this is the second volume of the suggested methods which describe borehole geophysics considering the present status of their utilization in rock engineering six types of geophysical methods used in boreholes velocity measurement along a borehole electric and electromagnetic logging nuclear logging vertical seismic profiling seismic tomography and resistivity tomography are described in addition since tunnels can be considered as boreholes seismic ahead of a tunnel face is also included in this volume because it has been often used in tunneling for each of the methods the following seven aspects of their deployment are described general applicability planning field operation data processing interpretation and output and report great emphasis is placed on aspects of planning and interpretation because they become more important in recent application of geophysics to rock engineering

isotope dating of waters at fram iii measurements of tritium helium 3 together with salinity yield 11 years as arctic basin residence time of the halocline waters in the arctic outflow in the fram strait radiocarbon and tritium data on the deeper waters point at some penetration of surface waters down to 1500 m during the last 20 years even at 2500 m the 14c activity is within 1 80 years of modern pre bomb values

planktonic foraminiferal depth habitat and δ18o calibrations plankton tow results from the atlantic sector of the southern ocean varies by several orders of magnitude across a large gradient in sea surface temperature and other hydrographic features demonstrating high sensitivity of foraminiferal populations to regional differences in water properties the depth of maximum abundance for key species such as globigerina bulloides and neogloboquadrina pachyderma is not constant from station to station the pattern suggests that their abundance and shell chemistry are tied to density horizons or other conditions such as food availability that become more sharply defined with depth in the northern subantarctic the consistent observation of globorotalia inflata and globoratalia truncatulinoides as relatively deep dwelling species confirms their utility as indicators of upper thermocline properties in d 18 o all species are observed to be isotopically lighter than predicted from water properties but the species specific offset is fairly uniform at all stations these observations define the utility of multispecies d 18 o for reconstructing temperature and density stratification from past surface oceans index terms 4267 oceanography general paleoceanography 4572 oceanography physical upper ocean processes 4870 oceanography biological and chemical stable isotopes 3030 marine geology and geophysics micropaleontology keywords stratification d 18 o

climate and oceanographic variability in the sw barents sea during the holocene the holocene section of the marine sediment core psh 5159n located in the sw barents sea has been studied at high resolution with a multiproxy approach a well stratified water column occurred at the site 11 9 8 ka bp the stratification was probably a result of a winter sea ice cover and or fresh warm surface waters during summer stratification and resultant reduction in air sea interaction allowed for warmer bottom water temperatures the general situation 11 9 8 ka bp could have been associated with an anomalous high pressure system over the nordic seas and the arctic ocean during the 11 10 5 ka bp interval the polar front was located close to the barents sea margin the polar front moved towards the site from 10 5 ka bp and from 9 8 to 7 5 ka bp it was probably located close to the site at 7 5 ka bp the polar front retreated eastwards as the present day oceanographic pattern established the mid holocene was in general characterized by rather stable conditions in contrast highly variable cond

comparison of geoelectrical imaging and tunnel documentation at the hallandsas tunnel sweden article i nfo for construction in rock a thorough pre investigation is important in order to avoid unforeseen conditions which may delay the work it is crucial to remember the results from this investigation in the further work and use the experience from the construction to update the geological prognosis and reduce the uncertainties different geophysical methods have proved valuable tools in such investigations in this work the electrical imaging is evaluated with regards to the method s applicability the evaluation is done qualitatively by comparing the electrical imaging with tunnel documentation from a tunnel in southern sweden by evaluating the result continuously when making the tunnel a more detailed geological prognosis can be compiled and used in the continued work with the tunnel the parameters used for the comparison are lithology q rqd weathering and water leakage the result was that virtually every change in electrical resistivity image coincides with a change in rock conditions the general trend was that high resistivity corresponded with good quality gneiss whereas low resistivity corresponds to poor quality rock e g high weathering low rqd low q and or several lithological contacts the intermediate resistivity is often amphibolites or rock with water bearing fractures the results were supported by in situ resistivity measurements inside the tunnel and resistivity logging in a core drilling geoelectrical imaging proved to give valuable information for a detailed geological model which could be compiled for a section where the tunnel had not yet been drilled as a help for planning of the continued tunnel work as is the case other geophysical methods it is clear that for the interpretation of data a priori information about the geological setting is necessary

the new col di tenda tunnel between italy and france integrated geological investigations and geophysical prospections for preliminary studies on the italian side abstract this paper illustrates the results of a multidisciplinary study led by the cnr italian national research council on the behalf of anas national road society for the preliminary phase for the excavation of the new col di tenda tunnel between italy and france surface geology of the col di tenda area north western italy piemonte region is characterized by a gently north dipping homocline composed of triassic marls jurassic limestones and eocene conglomerates calcarenites and claystones all belonging to the sub brianconnais geological domain these sedimentary sequences are cut by high angle normal faults and overthrust eocene sandstones and claystones of the delphinese geological domain along a south verging and north dipping thrust surface the sub surface setting was investigated by wells geoelectric sections and reflection seismic lines that pointed out a puzzling geological structure geoelectric sections in particular showed sharp lateral resistivity contrast and resistivity inversion at depth determined by variation in rock fracture density and in water circulation close to the main tectonic elements seismic lines were helpful to understand the geometric relationship between the jurassic neritic limestones and the eocene marly calcareous multilayer of the sub brianconnais domain and to exclude the presence of triassic evaporites of the delphinese domain along the tunnel alignment the acquired information allowed us to achieve a complete 2d structural model of the area the model demonstrated the most suitable route for the excavation of the new col di tenda tunnel among those proposed by the italian french inter governative committee

on the hydrography of the northeast water polynya the water masses and circulation in the area of the northeast water polynya located on the east greenland shelf north of 79 n are described on the basis of an r v polarstern cruise during spring and summer 1993 the baroclinic flow shows northward components close to the east greenland coast and eastward components at the northern limit of the polynya an anticyclonic half circle is formed by this and the southward flowing east greenland current in the south the circle is not closed the upper water column occupied by polar water is affected by this circulation pattern while deeper waters in the trough system of the area seem to spread independently different types of deep waters are found in different troughs all being of atlantic origin though they seem not to be directly connected to return atlantic water it is shown that what is called polar water must be formed at least partly on the greenland shelf and that deepwater formation does not occur in the investigated area

western equatorial pacific planktic foraminiferal fluxes and assemblages during a la nina year 1999 abstract a correlation between foraminiferal community dynamics and environmental conditions may provide a basis for establishing paleoclimatic proxies we studied planktic foraminiferal shell fluxes and assemblages in samples collected in three time series sediment trap deployments in the western equatorial pacific under la nina conditions from january to november 1999 eleven species contributed about 90 of the total flux in all traps two sites mt1 mt3 in the western pacific warm pool region wpwp were characterized by common occurrences of the species globigerinoides ruber globigerinoides sacculifer globigerinoides tenellus and neogloboquadrina dutertrei site mt5 farther to the east in the equatorial upwelling region had common occurrences of globigerina bulloides globigerinita glutinata and pulleniatina obliquiloculata very high abundances of g bulloides and g glutinata at mt5 indicate that equatorial upwelling eu occurred during the 1999 la nina the two western sites have similar assemblage compositions but mt1 135 e has the highest fluxes up to 3800 tests m 2 day 1 whereas mt3 145 e has fluxes below 2200 tests m 2 day 1 relatively high fluxes up to 3000 tests m 2 day 1 occur at site mt5 176 e where upwelling occurred the differences in faunal composition in the wpwp and eu might be attributable to differences in the way in which nutrients are supplied to the phytoplankton large amounts of suspended material are supplied to the wpwp by advection of waters passing through the coastal region of an archipelago whereas upwelling of nutrient rich waters enhances primary production in the eu at the westernmost site in the wpwp a peak in the g bulloides flux coincided with southward flow of the new guinea coastal current ngcc in late february but the highest g ruber flux coincided with northward flow of this current in late may thus the differences in species dominance at this location may be caused by monsoon driven variability in the flow direction of the nggc

glacial to deglacial changes in north atlantic meltwater advection and deep water formation centennial to millennial scale 14c records from the azores plateau abstract the last deglacial was marked by tremendous changes in ocean temperature and circulation as well as atmospheric co2 and 14c we employed the 14c plateau tuning technique to a centennial scale planktic 14c record of core md08 3180 retrieved s w of the azores islands at 3060 m water depth to establish both a new standard of absolute age control and a record of past 14c reservoir ages of ocean surface waters both 18o minima of g bulloides and high planktic reservoir ages of 1600 to 2170 yr suggest two major melt water incursions that reached from the labrador sea up to the subtropics over heinrich stadial 1 hs 1 in parallel we established a record of apparent benthic ventilation ages that add the planktic 14c reservoir ages together with the benthic planktic 14c age difference at the site and time of deposition a sum finally adjusted to past changes in atmospheric 14c that occurred since the time of deep water formation near the azores apparent deep water ages of the last glacial maximum were as low as 340 740 yr which suggests a lateral advection of young north atlantic deep waters nadw from subpolar regions south of iceland in harmony with recent model simulation and in contrast to a widely assumed major shoaling of glacial deep water formation during hs 1 local benthic ventilation ages increased up to 2200 2550 yr thus suggest an incursion of old southern source deep waters an unstable regime that was interrupted by brief pulses of nadw incursion near 16 15 6 cal ka and most salient near 14 9 14 7 ka

thermodynamic influences on the marine carbon isotope record air sea exchange represents an important controlling factor for the distribution of carbon isotopes in the modern ocean even below the surface mixed layer here we show that this thermodynamic influence varies between water masses with a magnitude which is large relative to the amplitude of typical deep sea sediment 13c records thus changes in air sea exchange processes must be regarded as a significant source of variability for any marine 13c signal

deepwater source variations during the last climatic cycle and their impact on the global deepwater circulation the degree of similarity of the 13c records of the planktonic foraminiferal species n pachyderma and of the benthic foraminiferal genus cibicides in the high latitude basins of the world ocean is used as an indicator of the presence of deepwater sources during the last climatic cycle whereas continuous formation of deep water is recognized in the southern ocean the norwegian sea stopped acting as a sink for surface water during isotope stage 4 and the remainder of the last glaciation however deep water formed in the north atlantic south of the norwegian sea during the last climatic cycle as early as isotope substage 5d and this area was also the only active northern source during stages 4 2 a detailed reconstruction of the geographic distribution of 13c in benthic foraminifera in the atlantic ocean during the last glacial maximum shows that the most important deepwater mass originated from the southern ocean whereas the glacial north atlantic deep water cannot be traced south of 40 n at shallower depth an oxygenated 13c rich intermediate water mass extended from 45 n to 15 s in the pacific ocean a ventilation higher than the modern one was also found in open ocean in the depth range 700 2600 m and is best explained by stronger formation of intermediate water in high northern latitudes

evidence for two step deglaciation and its impact on north atlantic deep water circulation oxygen and carbon isotope records from benthic and planktonic foraminifera are presented for the past 35 000 years in the northeastern atlantic the results support the idea that the last deglaci ation took place in two major steps1 4 and conflict with theories calling for a strong reduction in north atlantic deep water formation to explain the abrupt cooling of the younger dryas cold period5 7

climate correlations between greenland and antarctica during the past 100 000 years the ice cores recovered from central greenland by the grip1 2 and gisp23 projects record 22 interstadial warm events during the part of the last glaciation spanning 20 105 kyr before present the ice core from vostok east antarctica records nine interstadials during this period4 5 here we explore links between greenland and antarctic climate during the last glaciation using a high resolution chronology derived by correlating oxygen isotope data for trapped o2 in the gisp2 and vostok cores we find that interstadials occurred in east antarctica whenever those in greenland lasted longer than 2 000 years our results suggest that partial deglaciation and changes in ocean circulation are partly responsible for the climate teleconnection between greenland and antarctica ice older than 115 kyr in the gisp2 core shows rapid variations in the 18o of o2 that have no counterpart in the vostok record the age depth relationship and thus the climate record in this part of the gisp2 core appears to be significantly disturbed

stable isotopes in planktonic and benthic foraminifera from arctic ocean surface sediments oxygen and carbon isotopic analyses have been performed on the tests of planulina wuellerstorfi and three size fractions of sinistral neogloboquadrina pachyderma recovered from 33 arctic ocean surface sediment samples stable isotopic compositions of n pachyderma are found to be dependent on the test size larger specimens show considerable enrichment in both 18o and 18c the difference between the isotopic compositions of the 63 125 and 125 250 m size fractions in n pachyderma can be explained by biogenic fractionation effects during foraminiferal test growth larger 250 500 m n pachyderma displayed accretions of secondary calcite i e the outermost shell contained significant amounts of inorganically precipitated magnesium calcite thus larger foraminifera may not be suited for down core stable isotopic studies there is a difference of 2 between 18o values of surface samples from the eastern and western arctic ocean reflecting large differences between surface water salinity in these re

seasonal stable isotopic variations in living planktonic foraminifera from bermuda plankton tows abstract seasonal variations in surface water temperature and the 18o 16o ratios of calcite tests of living planktonic foraminifera collected in the upper 10 mare are coincident in the sargasso sea off bermuda the 18o of seasonally restricted globorotalia truncatulinoides and globigerinoides ruber pink and white may be used to determine the seasonal temperature contrast of the oceans in the past a preliminary model based on yearly absolute abundance and isotopic composition of these two species is able to approximate the composite 18o of fossil specimens of these species carbon and oxygen isotopic compositions of most species are size dependent with the largest differences occuring in 13c as a function of size the calcite tests of all living species were depleted in 13c relative to the 13c of total dissolved co2 at 0 and 50 m with no seasonal pattern in 13c being discernible in any species in almost all cases fossil specimens from box core sediments are significantly enriched in 13c and slightly enriched in 18o relative to their counterparts in the living fauna because the sediment populations are generally composed of larger sized specimens compares to the plankton of larger size specimens compared to the plankton

late quaternary paleochemistry of high latitude surface waters recent studies have stressed the role of high latitude nutrient levels and productivity in controlling the carbon isotopic composition of the deep sea and the co2 content of the atmosphere we undertook a study of the chemical composition of the polar planktonic foraminifer neogloboquadrina pachyderma s sinistral coiling from 30 late holocene samples and 49 down core records from the high latitude north and south atlantic oceans to evaluate the history of sea surface chemical change from glacial to interglacial time stable isotopic analysis of coretop samples from the atlantic pacific and southern oceans shows no significant correlation between the 13c of n pachyderma and either 13c or po4 in seawater conversely cd ca ratios in planktonic foraminifera are consistent with the po4 content of surface waters the level of maximum glaciation 18 000 yr b p identified by climap and 18o was chosen for mapping isopleths of 18o on n pachyderma s in the north atlantic reveal a pattern largely influenced by sea surface temperature s s t and generally support the s s t reconstruction of climap differences between the two suggest significantly lower salinity in north atlantic surface waters at high latitudes than in lower latitudes down core 13c records of n pachyderma confirm that low 13c values occurred in the northeast atlantic during the latest glacial maximum labeyrie and duplessy 1985 however a map of 13c for the 18 000 yr b p level for a much larger region in the north atlantic shows that minimum n pachyderma 13c occurred in temperate waters n pachyderma 13c decreased toward the southwest reaching a minimum of 1 at 37 n despite the variability seen in 13c records of n pachyderma none of our cores show significant temporal variability in cd ca from the combined cd ca and 13c data we can see no evidence for an upwelling gyre in the eastern north atlantic during the latest glacial maximum nor evidence that the southern and northern oceans had significantly different levels of preformed nutrients than today

stable isotope data and depositional environments in the late quaternary arctic ocean there has been much speculation about the history of the arctic ocean particularly its response to the late quaternary climatic fluctuations1 8 as a result considerable data have been gathered from arctic ocean sediment cores to reconstruct glacial and interglacial arctic ocean palaeoenvironments8 9 but even with these data the reconstructions and the correlations with the quaternary chronostratigraphy have been unsatisfactory mainly because of the lack of detailed stratigraphical data such as those provided by stable oxygen isotope stratigraphy10 here we present stable isotope records from arctic ocean sediment cores which can be correlated convincingly with corresponding data from the north atlantic together with lithostratigraphical data they provide new evidence on arctic ocean history in relation to global late quaternary climatic fluctuations

stable isotope studies of planktonic foraminifera in north atlantic core tops abstract stable isotope analyses of eight species of planktonic foraminifera from 42 north atlantic core tops are used to calculate isotopic depth ranges these depth ranges agree quite well with those based on plankton tows suggesting that no significant departures from oxygen isotopic equilibrium occur in most species reasonable isotherm patterns can be obtained from the 18 o data and the range in 18 o values between species is a useful indicator of the boundary of the subtropical gyre

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

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

simmax a modern analog technique to deduce atlantic sea surface temperatures from planktonic foraminifera in deep sea sediments we present a data set of 738 planktonic foraminiferal species counts from sediment surface samples of the eastern north atlantic and the south atlantic between 87 n and 40 s 35 e and 60 w including published climate long range investigation mapping and prediction climap data these species counts are linked to levitus s 1982 modern water temperature data for the four caloric seasons four depth ranges 0 30 50 and 75 m and the combined means of those depth ranges the relation between planktonic foraminiferal assemblages and sea surface temperature sst data is estimated using the newly developed simmax technique which is an acronym for a modern analog technique mat with a similarity index based on 1 the scalar product of the normalized faunal percentages and 2 a weighting procedure of the modern analog s ssts according to the inverse geographical distances of the most similar samples compared to the classical climap transfer technique and conventional mat techniques simmax provides a more confident reconstruction of paleo ssts correlation coefficient is 0 994 for the caloric winter and 0 993 for caloric summer the standard deviation of the residuals is 0 90 c for caloric winter and 0 96 c for caloric summer at 0 m water depth the sst estimates reach optimum stability standard deviation of the residuals is 0 88 c at the average 0 to 75 m water depth our extensive database provides sst estimates over a range of 1 4 to 27 2 c for caloric winter and 0 4 to 28 6 c for caloric summer allowing sst estimates which are especially valuable for the high latitude atlantic during glacial times an electronic supplement of this material may be obtained on adiskette or anonymous ftp from kosmos agu org login toagu s ftp account using anonymous as the username and guestas the password go to the right directory by typing cd append typels to see what files are available type get and the name of the file toget it finally type exit to leave the system paper 95pa01743 simmax a modern analog technique to deduce atlantic sea surfacetemperatures from planktonic foraminifera in deep sea sediments uwepflaumann josette duprat claude pujol and laurent d labeyrie diskette may be ordered from american geophysical union 2000florida avenue n w washington dc 20009 payment mustaccompany order

oceanic evidence for coherent fluctuations in fennoscandian and laurentide ice sheets on millennium timescales proxy temperature records from greenland ice cores1 2 and north atlantic sediment cores3 have provided evidence for a high degree of climate instability during the last glacial period much of this variability seems to be linked with the dynamics of the laurentide ice sheet that covered north america at this time3 which dis charged iceberg flotillas into the north atlantic that are now recorded in sediment cores as heinrich events4 how if at all this variability was manifested on the other side of the atlantic in the nordic seas and the ice sheets of northwest europe and scandinavia has been unclear here we present sediment micro fossil and oxygen isotope data from a sediment core in the norweg ian sea which reveal cooling events and iceberg discharges analogous to heinrich events we show that these climate fluctua tions in the norwegian sea were in phase or were phase locked with air temperatures over greenland suggesting that the rapid changes in heat fluxes in the north atlantic recorded in previous records3 were felt in this high latitude region the iceberg dis charges in our record seem to have come from the fennoscandian ice sheet implying that this and the laurentide ice sheets fluctu ated coherently on timescales shorter than those of milankovitch orbital cycles

late glacial and holocene palaeoceanography of the north icelandic shelf high resolution gravity cores and box cores from the north icelandic shelf have been studied for palaeoceanographic history based on lithological and biostratigraphical foramin iferal data results from two outer shelf cores covering the last 13 6 k 14 c yr bp are presented in this paper the sediments accumulated in north south trending basins on each side of the kolbeinsey ridge at water depths of ca 400 m sedimentation rates up to 1 5 m kyr 1 are observed during the late glacial and holocene the vedde and saksunarvatn tephras are present in the cores as well as the hekla 1104 a new tephra kol gs 2 has been identified and dated to 13 4 k 14 c yr bp and another tephra geochemically identical to the borrobol tephra has been found at the same level at present the oceanographic polar front is located on the north icelandic shelf which experiences sharp oceanographic surface boundaries between the cold east icelandic current and the warmer irminger current past changes in sedimentological and biological processes in the study area are assumed to be related to fluctuations of the polar front the area was deglaciated before ca 14 kyr bp but there is evidence of ice rafting up to the end of the gs 1 greenland stadial 1 younger dryas period increasing again towards the end of the holocene foraminiferal studies show a relatively strong gs 2 pre 13 kyr bp palaeo irminger current followed by severe cooling and then by unstable conditions during the remainder of the gi 1 greenland interstadial 1 bolling allerod and gs 1 younger dryas another cooling event occurred during the preboreal before the holocene current system was established at about 9 kyr bp after a climatic optimum between 9 and 6 kyr bp the climate began to deteriorate and fluctuate copyright 2000 john wiley sons ltd

insights into north atlantic deep water formation during the peak interglacial interval of marine isotope stage 9 mis 9 foraminifera abundance and stable isotope records from odp site 984 61 25 n 24 04 w 1648 m in the north atlantic are used to reconstruct surface circulation variations and the relative strength of the north atlantic deep water nadw formation over the period spanning the peak warmth of marine interglacial stage mis 9e 324 336 ka this interval includes the preceding deglaciation termination 4 t4 and the subsequent glacial inception of mis 9d the records indicate a greatly reduced contribution of nadw during t4 as observed in more recent deglaciations in contrast with the most recent deglaciation the lack of a significant nadw signal extended from t4 well into the peak interglacial mis 9e and persisted nearly until the transition to the subsequent glacial stage mis 9d although nadw formation resumed during mis 9e only depths greater than 2000 m appear to have been ventilated the poorly ventilated intermediate depth of site 984 2000 m may have resulted on one hand from a general reduction of deep water ventilation by nadw during the study interval or on the other hand from different pathways of the spread of newly formed nadw that bypassed the study location the intermediate depths may have also been invaded by southern sourced waters as the formation of intermediate depth nadw weakened the absence of any significant nadw signal at the water depth of site 984 during the climatic optimum contrasts sharply with subsequent interglacial peaks mis 5e and the holocene despite the perturbed intermediate depth circulation oceanic heat transport northeastward was not interrupted and may have contributed to the relatively mild interglacial conditions of mis 9e

a salt oscillator in the glacial atlantic 1 the concept as shown by the work of dansgaard and his colleagues climate oscillations of one or so millennia duration punctuate much of glacial section of the greenland ice cores these oscillations are characterized by 5 c air temperature changes severalfold dust content changes and 50 ppm co2 changes both the temperature and co2 change are best explained by changes in the mode of operation of the ocean in this paper we provide evidence which suggests that oscillations in surface water conditions of similar duration are present in the record from a deep sea core at 50 n based on this finding we suggest that the greenland climate changes are driven by oscillations in the salinity of the atlantic ocean which modulate the strength of the atlantic s conveyor circulation

high resolution climate records from the north atlantic during the last interglacial the two deep ice cores recovered by the grip1 and gisp22 projects at summit greenland agree in detail over the past 100 000 years3 and demonstrate dramatic climate variability in the north atlantic region during the last glacial before the current period of holocene stability this glacial climate instability has subsequently been documented in the marine sedimentary record of surface ocean conditions in the north atlantic4 before 100 kyr ago the two ice core records are discrepant however casting doubt on whether the oxygen isotope fluctuations during the last interglacial eemian seen in the grip core1 5 represent a true climate signal here we present high resolution records of foraminiferal assemblages and ice rafted detritus from two north atlantic cores for the interval 65 kyr to 135 kyr ago extending the surface ocean record back to the eemian the correlation between our records and the greenland ice core records is good throughout the period in which the two ice cores agree suggesting a regionally coherent climate response during the eemian our marine records show a more stable climate than that implied by the grip ice core suggesting that localized phenomena may be responsible for the variability in the latter record during the eemian

stable isotope clue to episodic sea ice formation in the glacial north atlantic sea ice is a determinant parameter of the climate system which acts as amplifier through positive ice albedo feedbacks and induces deep water formation through brine production it is also one of the most elusive parameters in the paleoclimate record most proxies of sea ice provide information on its presence and extent of e g diatoms or dinocysts but do not permit assessment on its rate of formation however seemingly off equilibrium low 18o values in mesopelagic planktic foraminifer species as observed today in the arctic ocean are thought to relate to the production of isotopically light brines during sea ice formation and might thus provide a clue on the rate of sea ice growth with reference to the isotopic properties of modern planktic foraminifers in the arctic ocean and using multi proxy data sets from the last glacial stage in the northwest north atlantic we re examined some of the current interpretations of planktic isotope records in the glacial nw north atlantic the large amplitude light isotopic excursions recorded in neogloboquadrina pachyderma left coiling during heinrich events 1 for example correspond to extensive sea ice cover as reconstructed from dinocysts and do not seem unequivocally linked to low salinity pulses such light isotopic excursion more likely responded to enhanced rates of sea ice formation resulting in the production and sinking of isotopically light brines on the contrary the isotopically heavy planktic foraminifers of the last glacial maximum lgm interval stricto sensu would rather suggest relatively low rates of brine production thus low sea ice growth rates in the area this would imply that the lgm distribution of sea ice in the north atlantic was primarily linked to spreading and drifting from marginal and nordic source areas and not from enhanced in situ production at the scale of glacial interglacial cycles isotopic distillation processes relating to sea ice production at high latitudes could be one of the factors controlling the 18o salinity relationship in deep ocean water masses that might deserve closer examination as it would be independent of continental ice volume changes

oxygen isotope compositions of sinistral neogloboquadrina pachyderma tests in surface sediments north atlantic ocean abstract neogloboquadrina pachyderma left coiled is a planktonic foraminifer indicator species for polar waters it is present in both the glacial and interglacial sediments of the high latitude oceans and therefore is frequently used as a signal carrier for constructing late pleistocene holocene planktonic 18 o records in this study the 18 o compositions of n pachyderma l tests from deep sea surface sediments are compared with surface water 18 o values and summer sea surface temperatures sst in the north atlantic ocean the norwegian greenland sea and the labrador sea we document that for a temperature range of 2 8 c the planktonic 18 o values follow paleotemperature equations with an offset of less than 0 4 and that above 8 c the planktonic 18 o compositions become almost independent of sst and remain nearly constant this pattern suggests that n pachyderma l precipitates its shell nearly at isotopic equilibrium with surface waters colder than 8 c and that in warmer surface waters n pachyderma l changes its habitat depth or its growth season to secrete its shell at an ambient temperature around 7 9 c

carbon isotope composition of tropical surface water during the past 22 000 years carbon isotope values of many species of planktonic foraminifera are size dependant values of 13c of individual size fractions are therefore an integration of low 13c values of calcite precipitated in the juvenile growth stage and high values precipitated in later stages in general the selection of a particular size fraction for downcore studies has been subjective analysis of different size fractions of planktonic foraminifera however yields different time series in downcore studies by measuring the 13c of many size fractions the 13c precipitated throughout the growth of the foraminifera can be calculated time series of the 13c of calcite precipitated in the late growth stages of planktonic foraminifera from two nearby cores from the caribbean sea result in a better correlation than time series of constant size fractions these 13c records indicate similar 13c values during the last glaciation and the late holocene and a broad deglacial minimum approximately synchronous with a minimum in the 13c records of benthic foraminifera from intermediate depth atlantic cores the deglacial minimum may be a reflection of the isotopic composition of the underlying intermediate water which may be affected by circulation changes or changes in preformed 13c values and or of the flux of water upwelled into the surface layer the small 0 2 to 0 0 glacial interglacial 13c difference in tropical surface water is also believed to be affected by the chemistry of the underlying source water

oceanic mechanisms for amplification of the 23 000 year ice volume cycle situated adjacent to the largest northern hemispher ice sheets of the ice ages the mid latitude north atlantic ocean has an important role in the earth s climate history it provides a significant local source of moisture for the atmosphere and adjacent continents forms a corridor that guides moisture bearing storms northward from low latitudes and at times makes direct contact along its shorelines with continental ice masses evidence of major ice ocean air interactions involving the north atlantic during the last 250 000 years is summarized outflow of icebergs and meltwater initially driven by summer insolation over the ice sheets affects midlatitude ocean temperatures summer heat storage winter sea ice extent and global sea level these oceanic responses in turn influence the winter moisture flux back to the ice sheets as well as ablation of land ice by calving spectral data indicate that the oceanic moisture and sea level feedbacks in part controlled by glacial melt products amplify milankovitch insolation forcing of the volumetrically dominant mid latitude ice sheets at the 23 000 year precessional cycle

modeling the distribution and seasonality of neogloboquadrina pachyderma in the north atlantic ocean during heinrich stadial 1

temperature reconstructions for sw and n iceland waters over the last 10 cal ka based on δ18o records from planktic and benthic foraminifera abstract we have obtained 18 o carb data from planktic n pachyderma s and benthic foraminifera c lobatulu s m barleeanu s from eight cores between 40 and 500 m water depth along the sw core b997 347 and n iceland margins cores b997 321 324 327 328 329 330 and 332 that span the last 10 cal ka sampling resolution varies between centuries to millennial scales over this time range changes in 18 o carb in foraminifera are the product of changes in the global ice volume and the temperature and salinity of the water at the level in which the foraminifera live in order to evaluate the relative roles of these variables we investigate 1 the salinity s and 18 o water values for present day waters off iceland and 2 the present day relationships between 18 o carb or calcite values of foraminifera and water column temperature and salinity data we estimate the average error in the temperature estimate to be 0 3 c based on a monto carlo simulation of the various error terms we argue that around iceland the variations in 18 o carb of both benthic and planktic species over the last 10 cal ka are principally controlled by temperature variations while salinity changes prove less important spatial and temporal changes are examined for both bottom water and 50 m water temperature reconstructions based on six and four cores respectively reconstructed temperatures for sites around sw n iceland indicate that surface and seafloor water temperatures were warmest in the early holocene 10 6 cal ka beginning at 6 cal ka surface and seafloor temperatures began to cool in n iceland and to become less stratified in sw iceland over the last 5000 yrs sea surface temperature variations have been 1 c for 50 of the observations with a maximum range of 2 5 c a profound decrease in temperature of 1 5 c is recorded in our fjord site b997 328 during the little ice age an abrupt earlier cold event is well expressed in at least three n iceland cores around 5 cal ka

vertical distribution and isotopic fractionation of living planktonic foraminifera from the panama basin a model1 2 which explains the vertical and seasonal distribution of planktonic foraminifera was developed using data from the western north atlantic and is comprised of three tenets 1 the conditions in the photic zone upper 80 100 m exclusively dictate planktonic foraminifera species composition and abundance throughout the water column 2 species are vertically stratified within the photic zone according to their temperature preference depth distribution according to temperature preference has been proposed by several authors3 based on isotope analyses of sediments due to seasonal temperature variations seasonal variations in the 18o composition of seawater and species specific isotope fractionation rigorous proof of this hypothesis cannot be provided from sediment analyses alone 3 the chlorophyll maximum is a major food source zone which is preferentially exploited by foraminifera our data from the panama basin which are presented here are confirmation of this model the panama basin in the eastern equatorial pacific which has a shallow and steep thermocline was sampled for living planktonic foraminifera a multiple opening closing net and environmental sensing system mocness 4 was used to collect 13 sets of eight vertically stratified oblique samples we report here the quantitative distribution and stable isotopic composition of planktonic foraminifera from four mocness tows taken over 5 days during august 1979 rv knorr cruise 73 at 5 20 n 8 50 w each tow consisted of eight samples which integrated 12 5 m intervals from 0 to 100 m for moc 126 25 m intervals from 0 to 200 m for moc 127 100 150 m intervals from 0 to 1 000 m on moc 128 and 250 m intervals from 0 to 2 000 m on moc 131

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation 1 abrupt decreases of the atlantic meridional overturning circulation moc during the late pleistocene have been directly linked to catastrophic discharges of glacimarine freshwater triggering disruption of northward marine heat transport and causing global climate changes here we provide measurements of excess sedimentary 231 pa 230 th from a high accumulation sediment drift deposit in the ne atlantic that record a sequence of sudden variations in the rate of moc associated deep ocean ventilation and surface ocean climatology the data series reveal a sequential decrease in the moc rate at 18 0 ka bp ago that coincides with only transient and localized freshwater inputs this change represents a substantial though not total cessation in moc that predates the major heinrich h1 meltwater event by at least 1 200 years these results highlight the potential of targeted freshwater perturbations in promoting substantial moc changes without a direct linking with catastrophic freshwater surges citation hall i r s b moran r zahn p c knutz c c shen and r l edwards 2006 accelerated drawdown of meridional overturning in the late glacial atlantic triggered by transient pre h event freshwater perturbation geophys res lett 33 l16616 doi 10 1029 2006gl026239

melting history of antarctica during the past 60 000 years marked changes in the surface water hydrology of the southern ocean during the past 60 kyr are revealed by a detailed comparison of the oxygen isotopic composition of planktonic and benthic foraminifera from sediment cores and the surface water temperature estimated by a transfer function derived from the distribution of diatoms in the same sediments from 35 to 17 kyr bp the southern ocean polar front was covered by a melt water lid containing a significant contribution from melting icebergs calved from antarctic ice shelves these icebergs may have originated from a succession of surges of the ice shelves

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

interglacial instability of north atlantic deep water ventilation disrupting north atlantic deep water nadw ventilation is a key concern in climate projections we use sub centennially resolved bottom water 13c records that span the interglacials of the last 0 5 million years to assess the frequency of and the climatic backgrounds capable of triggering large nadw reductions episodes of reduced nadw in the deep atlantic similar in magnitude to glacial events have been relatively common and occasionally long lasting features of interglacials nadw reductions were triggered across the range of recent interglacial climate backgrounds which demonstrates that catastrophic freshwater outburst floods were not a prerequisite for large perturbations our results argue that large nadw disruptions are more easily achieved than previously appreciated and that they occurred in past climate conditions similar to those we may soon face

supplementary data for rb sr and u pb geochronology and distribution of rock types in the precambrian basement of missouri and kansas most of what we know about basement rocks in kansas and missouri is derived from cores and cuttings from deep drilling these rocks may be divided into a northern terrane underlain by rocks consisting of abundant granite commonly showing cataclastic textures and by metavolcanic to metasedimentary rocks and a southern terrane underlain almost exclusively by rhyolitic flows and ash flow tuffs and epizonal granite plutons the northern terrane is interrupted in central kansas by mafic igneous rocks and flanking arkosic sedimentary rocks of the central north american rift system

stable oxygen and carbon isotopes in planktonic foraminifera neogloboquadrina pachyderma in the arctic ocean an overview of published and new surface sediment data abstract a summary study on oxygen and carbon stable isotopes in planktonic foraminifera from arctic ocean floor appeared in marine geology 20 years ago spielhagen and erlenkeuser 1994 we revisit this topic with a wealth of new data focused on the western amerasian arctic a spotlight in the current climatic and oceanic change neogloboquadrina pachyderma the most abundant polar planktonic foraminiferal species is an important tool for reconstructing surface subsurface water changes in the arctic our new data on n pachyderma 150 250 m from the surface sediments show 18 o and 13 c values of 18 o and 13 c are both influenced by complex water sources water column structure and foraminiferal depth habitat the observed distribution of n pachyderma stable isotopes confirms a shallow habitat of this species in the sea ice covered central arctic especially in the canada basin probably in relation to the shallow chlorophyll maximum the associated light n pachyderma 18 o reflects the long term storage of fresh water at the shelf break a deeper dwelling of n pachyderma with heavier 18 o is supported by a more extensive photic zone and nutrient availability air sea exchange plays an important role in 13 c distribution and is consistent with heavy n pachyderma 13 c in the perennially ice covered central arctic ocean light 13 c composition at the shelf break is additionally influenced by shelf bottom waters enriched in isotopically light remineralized terrestrial carbon distribution of foraminiferal 13 c on the chukchi shelf reflects primary production patterns in the area

millennial scale variability to 735 ka high resolution climate records from santa barbara basin ca 1 determining the ultimate cause and effect of millennial scale climate variability remains an outstanding problem in paleoceanography partly due to the lack of high resolution records predating the last glaciation recent cores from santa barbara basin provide 2500 5700 year windows of climate with 10 50 year resolution ages for three cores determined by seismic stratigraphic correlation oxygen isotope stratigraphy and biostratigraphy date to 293 ka mis 8 450 ka mis 12 and 735 ka mis 18 these records sample the late pleistocene during which the 100 kyr cycle strengthened and the magnitude of glacial interglacial cyclicity increased thus these records provide a test of the dependence of millennial scale behavior on variations in glacial interglacial cyclicity the stable isotopic 18o composition of planktonic foraminifera shows millennial scale variability in all three intervals with similar characteristics duration cyclicity to those previously documented during mis 3 at this site stadial g bulloides 18o values are 2 75 1 75 average 2 25 and interstadial values are 1 75 0 5 average 1 with rapid decadal scale interstadial and stadial initiations of 1 2 as in mis 3 interstadials lasted 250 1600 years and occurred every 650 1900 years stadial paleotemperatures were 3 5 9 5 c and interstadial paleotemperatures were 7 5 13 c upwelling evidenced by planktonic foraminiferal assemblages and 13c increased during interstadials similar to mis 3 high productivity during some stadials was reminiscent of the last glacial maximum this study builds upon previous records in showing that millennial scale shifts were an inherent feature of northern hemisphere glacial climates since 735 ka and they remained remarkably constant in the details of their amplitude cyclicity and temperature variability

neogloboquadrina pachyderma dex and sin mg ca and δ18o records from the norwegian sea magnesium calcium mg ca records based on n pachyderma dex and n pachyderma sin from the last 1200 years have been retrieved from high resolution cores in the norwegian sea comparing temperatures inferred from mg ca and the oxygen isotopic composition of calcite 18oc with instrumental temperature records from ocean weather ship mike suggests that n pachyderma calcifies during the summer season with an offset to oxygen isotope equilibrium of 0 6 in this region summer temperatures below the thermocline are related to the winter season ventilation and breakdown of the seasonal thermocline hence the deeper dwelling n pachyderma sin provides a winter season signal down core n pachyderma dex mg ca temperatures display larger variance than observed in 18oc temperatures record derived from the same morphotype the smaller variance in the 18ocn pachyderma dex temperatures is probably linked to salinity changes in the upper 50 m of the water column the mg ca temperature and 18oc records are used to reconstruct changes in the oxygen isotopic composition of water 18ow during the last 1200 years the reconstructed 18ow records show variation within a realistic range allowing the influence of other water masses than those present at the site today and suggest that the mg ca signal in morphotypes of n pachyderma in the norwegian sea responds to changes in climatic parameters

size dependent isotopic composition of planktic foraminifers from chukchi sea vs nw atlantic sediments implications for the holocene paleoceanography of the western arctic abstract in arctic and sub arctic seas shell growth and or secondary calcite overgrowth of neogloboquadrina pachyderma left coiled npl occur along the pycnocline and their 13c and 18o values are size and weight dependent however whereas the npl 18o data from the nw atlantic indicate near equilibrium conditions with ambient waters and a positive relationship between shell weight and 18o content assemblages from box cored sediments of the chukchi sea western arctic are depleted by 2 with respect to equilibrium values with modern conditions and depict a negative relationship between shell weight and its 18o value 0 15 0 03 g on vpdb scale a similar feature is also depicted by the dextral form of n pachyderma npd we associate the reverse shell size or weight vs 18o relationship to the reverse temperature gradient observed along the thermocline between the surface cold and dilute water layer and the underlying near 3 c warmer saline north atlantic water mass the analysis of two late to post glacial sedimentary sequences from the chukchi sea indicates that such a water mass stratification with a reverse thermocline persisted throughout the holocene thus reflecting an early onset of the modern like linkage between the arctic ocean and the north atlantic moreover lower 18o values in both npl and npd together with larger 18o gradients between the different shell sizes at ca 9 7 ka bp suggest 3 c higher temperatures in the upper north atlantic water mass in comparison with the present approximately 1 c at the study site thus likely a higher inflow rate of this water mass during the early holocene

predictive permeability model of extensional faults in crystalline and metamorphic rocks verification by pre grouting in two sub sea tunnels norway abstract this paper link quantitative fault zone descriptions qualitative fracture and fault rock properties and engineering data in the study of the permeability structure of fault zones datasets include scan lines drill cores and cement pre grouting from two sub sea tunnels in gneissic and granitic rocks from which systematic pre grouting volumes can be used to analyse the in site relative permeability both in host rocks and fault zones major extensional faults intersected by the tunnels reveal common fault rocks surrounding intensively fractured rock lenses in the core fracture frequencies in these lenses can reach 100 fractures metre f m in the bounding damage zones networks of fracture sets make up an inner zone of fairly high frequency 20 30 f m of fault parallel long fractures connected by shorter fractures an outer zone has lower frequencies tunnel scale injection of cement reveals patterns that can be ascribed to the impact of faulting there is an increase in cement injection in fault zones compared to areas with background fracturing away from faults in detail there is an innate division of the rock volume into sub zones characterized by distinct structural style and permeability with a background level and three fault related sub zones fault core inner damage zone and outer damage zone injection data shows that the background sub zone commonly can be injected with less than 0 05 m3 cement per metre tunnel commonly not injected whereas the fault core has permeability characteristics nearly as low as the outer damage zone represented by 0 1 0 2 m3 cement per metre tunnel with occasional peaks towards 0 5 m3 the maximum of cement injection lies in the inner damage zone marginal to the fault core with 0 3 0 7 m3 cement per metre tunnel locally exceeding 1 m3 this gives a relative relationship for cement injection of approximately 1 2 1 between fault core inner damage zone and outer damage zone of extensional fault zones in crystalline and metamorphic rocks

carbon isotopes and habitat of polar planktic foraminifera in the okhotsk sea the carbonate ion effect under natural conditions the upper 500 or 1000 m of the water column in the okhotsk sea was sampled for living planktic foraminifera the polar species neogloboquadrina pachyderma sinistral strongly dominates the foraminiferal assemblage the subpolar to temperate species globigerina bulloides accounts for 10 25 other species account for up to 3 only the shell 18o and 13c values of the species n pachyderma sin are compared to water 18o values and 13c values of dissolved inorganic carbon dic the strong gradient in 18o composition and temperature in the upper water column is reflected in the 18o of n pachyderma sin relative to the values expected for inorganic calcite precipitated under equilibrium conditions n pachyderma sin displays a vital effect of about 1 in 18o the 13c composition of n pachyderma sin is about constant with water depth and the reflection of 13cdic in the foraminiferal shell seems to be masked by other effects most foraminifera are found above or slightly below the thermocline and can be assumed to calcify in the upper 200 m of the water column the gradient of 13cdic extends well below this depth therefore the lack of correlation can partly be attributed to this fact the remaining discrepancy between 13c of n pachyderma sin and 13cdic correlates with the carbonate ion concentration in the water column this leads to the conclusion that the carbonate ion effect cie which has been derived from culturing experiments for other species spero et al 1997 nature 390 497 500 is found here under natural conditions when the magnitude of the cie derived for g bulloides is applied to n pachyderma sin cie corrected 13c of n pachyderma sin is a direct reflection of 13cdic in the water column with a constant offset of 1 2

combined electrical resistivity imaging and ground penetrating radar study for detection of buried utilities in federal university of agriculture abeokuta nigeria the knowledge of the exact location and depth of buried utility such as pipes assists greatly for prevention of accidents and wastage of resources this study addresses the application of integrated geophysical methods for detections of buried utility in student s residential hostels federal university of agriculture abeokuta southwestern nigeria the goals of the surveys are to determine the effectiveness of the applied methods in detection of buried utilities locations and their depths as well as verification of obtained depths to the top of target by excavation method 2d electrical resistivity imaging eri using wenner array with electrode separation ranging from 0 25 to 1 25 m and ground penetrating radar gpr survey using a common offset profiling and center frequency of 400 mhz were carried out along ten traverses in the study area the field data were processed using res2dinv and radan 7 softwares for resistivity and gpr data respectively inverted resistivity sections and radar images generated information up to a depth of 0 80 m and 3 00 m respectively the position size and depth of buried pipes cannot be determined precisely by ert compared to gpr survey the depths to the top of buried pipes by ert ranges from 0 20 to 0 46 m while the gpr measured depths ranged from 0 16 to 0 55 m from the surface integrated interpretation showed that gpr can effectively provide information about locations and depths to the top of buried pipes with a higher precision than ert method comparisons of measured gpr depths with in situ verification using excavation method correlate fairly well

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

global calibration of ecological models for planktic foraminifera from coretop carbonate oxygen 18 abstract a global dataset of coretop planktic foraminiferal 18oc is combined with a global database of seawater 18ow observations and ocean climatologies to determine robust optimum parameters for an ecological model for six commonly measured species and varieties these parameters consist of the temperature ranges optimum temperatures depth habitat and the amount of secondary calcification for globigerinoides ruber white g ruber pink neogloboquadrina pachyderma l n pachyderma r globigerinoides sacculifer and globigerina bulloides this approach produces ecological models and temperature ranges consistent with previous work and manages to reproduce the coretop oxygen 18 carbonate values remarkably well the standard error of modelled values of coretop calcite globally and for all species is 0 53 compared to an error of 1 2 when assuming annual average mixed layer equilibrium calcite

boat towed radio magnetotellurics a new technique and case study from the city of stockholm we have developed a new data acquisition system and technique to measure the radio magnetotelluric rmt signals from distant radio transmitters with the objective of mapping and modeling electric

changes in the oceanic 13c 12c ratio during the last 140 000 years high latitude surface water records detailed records of the carbon and oxygen isotopic ratios of neogloboquadrina pachyderma are compared between nine high latitude sediment cores from the northern and southern hemispheres covering the last 140 000 yrs the strong analogies between the 13c records permit to define a 13c stratigraphic scale with three clear cut transitions simultaneous with the oxygen isotopic transitions 65 125 kyrs 54 65 kyrs and 21 13 kyrs the 13c records of n pachyderma in the high latitude cores which follow the changes in 13c of the surface water tco2 near areas of deep water formation present trends similar to the benthic foraminifera 13c records in cores v19 30 and m12 392 although amplitudes of the isotopic shifts are different this implies that a large part of the observed variations represents global changes in the carbon distribution between biosphere and ocean the 13c12c ratios of n pachyderma in the north atlantic cores display larger regional variations at 18 kyrs b p than at present to explain these differences we have plotted the 18 kyrs b p 13c values of n pachyderma from 17 cores distributed n of 40 n comparison with published surface water temperature distribution at 18 kyrs b p indicates that a strong divergent cyclonic cell centered approximatively 55 n and 15 w was active during most of the last ice age maximum this hydrology analogous to the present weddell sea explains the published evidences of bottom water formation if located on the northern flank of the gyre and the strong polar front on the southern flank probable location of intermediate water formation

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

arctic ocean water mass balance from isotope data the distributions of the oxygen 18 and tritium isotopes and of salinity yield a residence time of 10 years for the surface and halocline waters of the arctic basin we find a yearly net production of 0 59 m of sea ice and an input of 1 16 m of freshwater from continental river runoff local precipitation and bering strait salinity deficiency using the basin area value with these numbers gives long term average total net production and transport rates of 0 15 sv of ice and 0 18 sv of meteoric component bering strait water not included if in addition a reasonable depth profile of relative current velocity is assumed for the outflow a yearly input of 2 8 sv of atlantic and bering strait water is needed to replenish the upper and halocline waters these numbers should be good to 20 and are multiyear averages the isotope data clearly indicate that the barents sea is an inflow area for atlantic water to the basin but that net export of ice occurs there

the late weichselian glaciation of the franz victoria trough northern barents sea ice sheet extent and timing high resolution seismic profiles parasound 4 khz and three sediment cores from the franz victoria trough and the adjacent continental slope were studied in order to constrain the timing and extent of the northern svalbard barents sea ice sheet during the late weichselian glaciation stacked debris flow lobes and layers of glacimarine diamicton on the lower continental slope indicate that large quantities of glacially derived sediments were deposited by the northern svalbard barents sea ice sheet directly onto the upper continental slope at approximately 23 14 c ka a grounding line advance to the shelf break is supported by the identification of diamicton interpreted as till in the seismic profile near the shelf break after several ice sheet instabilities marked by significant input of ice rafted detritus to the continental margin the disintegration of the northern svalbard barents sea ice sheet termination ia is indicated by a distinct pulse of ice rafted detritus at 15 4 14 c ka and the transition to an isotopically defined meltwater signal the drastic change in sedimentary pattern on the upper continental slope dated to about 13 4 14 c ka is interpreted as grounding line retreat from the shelf edge a further stepwise retreat of the northern svalbard barents sea ice sheet is indicated by pulses of ice rafted detritus which appear to be contemporaneous with the onset of distinct ice rafting events in adjacent areas and pulses of glacimarine sedimentation in the southwestern barents sea q 2000 elsevier science b v all rights reserved

upwelling and productivity along the peru chile current derived from faunal and isotopic compositions of planktic foraminifera in surface sediments abstract we report on the spatial distribution of isotopic compositions of the two planktic foraminifera species globigerina bulloides and neogloboquadrina pachyderma dex and the faunal assemblages of planktic foraminifera in 91 surface sediment samples along the chilean continental slope between 23 s and 44 s both 13c and 18o data of n pachyderma dex show little variability in the study area north of 39 s the isotopic values of n pachyderma dex are heavier than those of g bulloides whereas south of 39 s this relation inverses this is indicative for a change from a well mixed deep thermocline caused by coastal upwelling north of 39 s to well stratified water masses in a non upwelling environment south of 39 s in addition the faunal composition of planktic foraminifera marks this change by transition from an upwelling assemblage north of 39 s to a high nutrient non upwelling assemblage south of 39 s which is characterized by decreased contributions of upwelling indicators such as g bulloides n pachyderma sin and globigerinita glutinata in general we can conclude that food and light rather than temperature are the primary control of the planktic foraminiferal assemblage between 23 s and 44 s off chile our data point to higher marine productivity at upwelling centers north of 25 s and at 30 33 s south of 39 s significant supply of nutrients by fluvial input most likely boosts the productivity

norwegian sea warm pulses during dansgaard oeschger stadials zooming in on these anomalies over the 35 41 ka cal bp interval and their impacts on proximal european ice sheet dynamics abstract the last glacial millennial climatic events i e dansgaard oeschger and heinrich events constitute outstanding case studies of coupled atmosphere ocean cryosphere interactions here we investigate the evolution of sea surface and subsurface conditions in terms of temperature salinity and sea ice cover at very high resolution mean resolution between 55 and 155 years depending on proxies during the 35 41 ka cal bp interval covering three dansgaard oeschger cycles and including heinrich event 4 in a new unpublished marine record i e the md99 2285 core 62 69 n 3 57s e we use a large panel of complementary tools which notably includes dinocyst derived sea ice cover duration quantifications the high temporal resolution and multiproxy approach of this work allows us to identify the sequence of processes and to assess ocean cryosphere interactions occurring during these periodic ice sheet collapse events our results evidence a paradoxical hydrological scheme where i greenland interstadials are marked by a homogeneous and cold upper water column with intensive winter sea ice formation and summer sea ice melting and ii greenland and heinrich stadials are characterized by a very warm and low saline surface layer with iceberg calving and reduced sea ice formation separated by a strong halocline from a less warm and saltier subsurface layer our work also suggests that this stadial surface subsurface warming started before massive iceberg release in relation with warm atlantic water advection these findings thus support the theory that upper ocean warming might have triggered european ice sheet destabilization besides previous paleoceanographic studies conducted along the atlantic inflow pathways close to the edge of european ice sheets suggest that such a feature might have occurred in this whole area nonetheless additional high resolution paleoreconstructions are required to confirm such a regional scheme

deep dwelling planktonic foraminifera of the northeastern pacific ocean reveal environmental control of oxygen and carbon isotopic disequilibria abstract we assess the utility of four species of living planktonic foraminifera as tracers of thermocline and intermediate water masses in the northern pacific ocean based on their water column distribution and shell isotopic composition assuming oxygen isotopic equilibria with the water column we infer apparent calcification depths this allows an estimate of apparent carbon isotopic disequilibria we then relax the assumption of oxygen isotopic equilibrium to examine habitat effects on kinetic disequilibrium processes in the california current left coiling neogloboquadrina pachyderma and globigerina calida calcify in the upper thermocline globorotalia scitula resides within the shallow salinity minumum potential density 25 1 26 7 while globoquadrina hexagona is associated with the deeper north pacific intermediate water 26 7 26 9 apparent carbon isotopic disequilibria corrected for oxygen isotopic disequilibria range from 1 0 1 9 in these asymbiotic species the carbon isotopic disequilibrium can be modeled as a single exponential function of temperature or a logarithmic function of potential food supply we infer that carbon isotopic disequilibrium increases with metabolic rate related to temperature and or food supply kinetic processes of oxygen and carbon isotopic disequilibria yields reasonable depth habitats if the slope of the oxygen carbon isotopic shift is about 0 35 consistent with culture data our finding of a link between environment metabolism and isotopic disequilibrium observed in oceanic settings suggests the potential to better reconstruct the structure and biological processes of the upper water column from geologic data

comparing proxies for the reconstruction of lgm sea surface conditions in the northern north atlantic abstract within the frame of the multiproxy approach for the reconstruction of the glacial ocean margo project sea surface conditions of the last glacial maximum lgm 23 19 ka were reconstructed using different proxies which were calibrated to a standardized modern hydrography in the north atlantic the revised lgm margo data set provides a comprehensive coverage including the nordic seas the data set includes reconstruction based on planktonic foraminifer assemblages dinocyst assemblages alkenone coccolithophorid biomarkers and mg ca ratios in planktonic foraminifers several hydrological features of the lgm north atlantic can be identified that are supported by all four proxies they include an extensive perennial sea ice cover along the eastern canadian and greenland margins seasonally ice free central north atlantic and norwegian sea and the winter sea ice limit being located at about 55 n all proxies also suggest significantly colder than modern sea surface conditions in the southeastern part of the north atlantic and a more zonal temperature pattern than at present with a steep sst gradient of the order of 10 c between 40 n and 45 n however in the nordic seas large discrepancies remain well above the level of uncertainty of the sst reconstructions these discrepancies might be related to stratification of the upper water mass linked to large annual amplitude of temperature with contrasting winter and summer conditions high interannual interdecadal variability or taphonomic processes affecting some of the proxies the average lgm sst in the nordic seas cannot at present be assessed with confidence however the existing evidence suggests that highly variable sea surface conditions and at least occasional advection of north atlantic waters may have characterised the glacial nordic seas

neogloboquadrina pachyderma sinistral coiling as paleoceanographic tracers in polar oceans evidence from northeast water polynya plankton tows sediment traps and surface sediments the abundance and chemistry of the planktonic foraminifera neogloboquadrina pachyderma sinistral coiling have long been used as tools for monitoring polar surface ocean changes and for correlating these changes to atmospheric and thermohaline circulation fluctuations however due to its remote habitat very little is known about how modern n pachyderma s respond to changing environmental conditions in the polar seas modern samples of n pachyderma s from the northeast water polynya provide a means for studying how environmental conditions affect the vertical distribution and chemistry of this species highest abundances of n pachyderma s were associated with the chlorophyll maximum in the surface 20 80 m where they are exploiting their primary food source evidence suggests that the addition of a calcite crust modifies the calcite tests of some n pachyderma s between 50 and 200 m increasing shell density and modifying shell chemistry the shell mass of encrusted forms is 3 4 times greater than the nonencrusted forms between 50 and 200 m the oxygen isotope composition of n pachyderma s shells increase by 1 5 in response to local water column gradients the 13c values of n pachyderma s are basically invariant with depth in this region are consistently 1 0 depleted in comparison with the 13c for equilibrium calcite and remain basically constant during the shell thickening process mass balance calculations suggest that encrustation occurs at all depths but abundance counts suggest that the process occurs mostly at the depth of the main pycnocline sediment fluxes of n pachyderma s occur during a 2 week bloom event and decrease to almost zero below complete ice cover the decoupling of the processes controlling abundances and shell chemistry explain the discrepancies between transfer function and isotopically derived paleotemperature estimates of surface conditions in some oceanic settings the ability of 18o to record surface ocean conditions will depend on vertical water column gradients as evidenced by the differences in core top calibrations between the north and south atlantic

the influence of air and sea exchange on the carbon isotope distribution in the sea we explore here the influence of the temperature dependence of isotope fractionation between atmospheric co2and ocean co2 on the distribution of carbon isotopes in the ocean this is accomplished by an analysis of departures from the expected redfield tie between po4 and 13c we find that for the surface ocean the temperature influence largely compensates for the biologic influence in the deep ocean the temperature influence imprinted at the sites of deepwater formation reduces somewhat the biologically induced difference between the carbon isotope ratios for deep waters produced in the northern atlantic and in the antarctic these same features are reproduced in the hamburg ocean model in order to assess the impact of changes in the ratio of ocean mixing rate to wind speed we have made a model run in which co2 exchange rates between air and sea were everywhere doubled as expected the influence of the thermodynamic effect on the oceanic carbon isotope distribution is magnified

response of the high latitude northern hemisphere to orbital climate forcing evidence from the nordic seas sediment cores from the nordic greenland iceland and norwegian seas provide evidence that this area acts as an initial responder to the forcing effect of orbitally driven changes in insolation on the climate system as postulated by j imbrie et al the 18 o record of the cores documents a widespread initial deglacial signal in the area between 15 and 13 ka 1000 yr before other deglacial signals from other parts of the northern hemisphere an even earlier meltwater event has been dated to 16 090 185 yr b p north of iceland at the initial rise of northern hemisphere insolation after the last glacial maximum during the period with lowered surface salinities the nordic seas were still cold reconstructions of the surface water conditions of the area show that as the summer insolation values of the northern hemisphere reached half of maximum values a sea ice free corridor opened along norway at 13 4 ka nearly contemporaneous fluctuations of the polar front and the sea surface temperatures with the insolation changes indicate that the nordic seas are very sensitive to insolation forcing especially in regions close to the sea ice margin a decrease in sea surface temperature and an increase in the areal extent of sea ice cover since 7 ka indicate that the area is currently on the way to glacial conditions supporting the predictions made earlier by j imbrie et al

calderas in the precambrian terrane of the st francois mountains southeastern missouri precambrian igneous rocks in the st francois mountains of southeastern missouri consist of silicic volcanic rocks mostly ash flow tuff which crop out mostly in the western and southwestern part of the region and epizonal granitic plutons which are mostly exposed in the northeastern part of the area these relations suggest that the exposures in the northeast are of a somewhat deeper part of the crust and that rocks there are now exposed because of west southwesterly tilting and beveling by erosion in the eastern st francois mountains the occurrence of a thick rhyolitic ash flow tuff grassy mountain ignimbrite and its distribution relative to a large high silica pluton butler hill granite suggest that the ash flow is the principal eruptive material of a caldera the butler hill caldera and that butler hill granite is the frozen magma chamber that was originally beneath it structural relations indicate that butler hill granite was emplaced into the volcanic rocks of the caldera during resurgent doming four small low silica plutons silvermine stono knoblick and slabtown granites are distributed peripherally to the butler hill granite and are interpreted as ring plutons emplaced along the ring fracture of the caldera or along arcuate intracaldera faults after resurgent doming and emplacement of butler hill granite more than 3 km of silicic volcanic rocks occupy a basinal structure in the western st francois mountains these rocks lie with angular unconformity upon up domed older rocks of the butler hill caldera along an arcuate zone of megabreccia and disturbed structure on the western margin of the older caldera this feature is interpreted as the topographic wall of a second caldera which lies to the west the occurrence of the thick taum sauk rhyolite stratigraphically about 3 km higher than the rocks involved in the megabreccias may indicate that there was yet another caldera formed in this western part of the st francois mountains

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

evidence from fram strait 78 n for early deglaciation recent syntheses of the history of the last northern hemisphere glaciation and deglaciation illustrate that understanding of the mechanisms and timing of deglaciation before approximately 12 000 years bp1 5 is limited after 12 000 yr bp however there is sufficient evidence from radiocarbon dated moraines raised beaches varved lake sediments and pollen records to provide a reasonable temporal and geographic picture of the decay of the ice sheets here we report on the first oxygen isotope record from the norwegian greenland sea that is radiocarbon dated directly by accelerator mass spectrometry a significant light oxygen isotope event is recorded at approximately 15 000 years bp which suggests that the marine based barents shelf ice sheet disintegrated rapidly at this time recent studies6 7 have estimated that the decay of this ice sheet could have contributed as much as 15 metres to eustatic sea level rise the decay of the barents shelf ice sheet is the earliest major deglacial event yet dated and may have triggered subsequent deglacial events through eustatic sea level effects

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

spatial predictions of geological rock mass properties based on in situ interpretations of multi dimensional seismic data abstract the article presents a statistical approach to characterize and predict engineering geological conditions in the up to 2000 m deep faido tunnel and gotthard base tunnel in switzerland seismic investigations were conducted to improve the technology of interpreting seismic tomographic images overall the goal of this study was to predict spacial maps of geological rock mass properties such as uniaxial compressive strength or total fracture spacing by using up to six seismic features in combination e g compression wave and shear wave velocities and dynamic poisson s ratio self organizing mapping som an artificial intelligent method was used for the purposes of interpreting multi dimensional geophysical attributes derived from seismic profiles of tomographic images along tunnel sidewalls the som method was applied in the faido tunnel to delineate complex physical relations between the geological and seismic parameters then the method was applied to predict geological properties around a segment of the gotthard base tunnel with unknown geological geotechnical conditions the results illuminate that correlation analyses pairwise parameter classification are substantially less powerful than the som method multi parameter classification in order to interpret geological features from seismic in situ data moreover predicted spatial distributions of the total fracture spacing and the uniaxial compressive strength for example corresponded well with drill core and tunnel mapping results the som approach was a helpful tool for practitioners in predicting zones of instabilities and geological complexity during underground excavation processes of the gotthard base tunnel it is suggested to use such an interpretation method as decision support for purposes of sub surface exploration and long term geophysical monitoring of large scale geoengineering projects such as disposals of nuclear waste and greenhouse gases or geopower plants for renewable energy geothermal biosoils

north atlantic deep water and climate variability during the younger dryas cold period the younger dryas the last large millennial scale climate oscillation 12 9 11 6 ka has been widely attributed to a massive meltwater discharge event that disrupted ocean circulation and plunged the circum north atlantic back into a near glacial state low resolution deep water reconstructions indicate lower north atlantic deep water nadw production during the younger dryas though the 14 c record requires some deep water production herein we reconstruct deep water mass variations using a southern gardar drift sediment core with an expanded younger dryas section we show that southern sourced water invaded the deep north atlantic to start the younger dryas but was replaced by nadw within 500 yr southern sourced waters briefly reappeared at the end of the younger dryas these deep water reorganizations to start and end the younger dryas suggest that increased meltwater fluxes were limited temporally and focused on regions where deep water convection occurred during the deglaciation

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

structure of the upper water column in the northwest north atlantic modern versus last glacial maximum conditions 1 during the last glacial maximum the northwestern north atlantic constituted a major conduit for labrador and greenland ice sheet meltwaters vertical density gradients in its upper water masses have been reconstructed by combining information from transfer functions based on dinocysts and from oxygen isotope measurements 18o in planktonic foraminifera transfer functions yield temperature and salinity and thus potential density for the warmest august and coldest february months in the photic zone the 18o values in different size fractions of epipelagic globigerina bulloides and mesopelagic neogloboquadrina pachyderma left coiled npl foraminifera allow us to assess gradients through the pycnocline between surface and intermediate waters based on the calibration of a versus 18o relationship from transfer function reconstructions the size and density of npl shells provide further constraints on these gradients the results show the development of a very strong pycnocline during the lgm with a difference of about 3 summer to 1 5 winter units between surface and underlying waters they indicate conditions unfavorable for vertical convection and support the hypothesis of the spreading of a shallow low salinity buoyant layer over the northern north atlantic this layer depicted a strong e w gradient with maximum seasonal contrast and minimum absolute values westward

oceanographic changes through the last millennium off north iceland temperature and salinity reconstructions based on foraminifera and stable isotopes abstract temperature and salinity reconstructions for two 1000 year high resolution sedimentary records located at the boundary between atlantic and arctic surface waters on the north icelandic shelf are based on transfer functions and oxygen isotopes for planktonic and benthic foraminifera there is a general increase of arctic water indicator species at the transition from the medieval warm period into the little ice age lia and a subsequent return of atlantic water indicator species towards the end of the lia and in the 20th century the timing of the reconstructed temperature changes both at the beginning and at the end of the lia appears to be slightly different for the different water masses the earliest temperature change is seen in the bottom and subsurface waters where a cooling is reconstructed as early as ad 1150 1200 at both locations whereas previously published diatom based and alkenone based sea surface temperature reconstructions show a change at ad 1300 coinciding with the air temperature shift in the area our results show the need of a thorough understanding of the oceanography in the study area as well as the different living habitat for the biological proxies used for the temperature estimates

a global compilation of late holocene planktonic foraminiferal δ18o relationship between surface water temperature and δ18o we review the different sources of uncertainty affecting the oxygen isotopic composition of planktonic foraminifera and present a global planktonic foraminifera oxygen isotope data set that has been assembled within the margo project for the late holocene time slice the data set consists of over 2100 data from recent sediment with thorough age control that have been checked for internal consistency we further examine how the oxygen isotopic composition of fossil foraminifera is related to hydrological conditions based on published results on living foraminifera from plankton tows and cultures oxygen isotopic values 18o of margo recent fossil foraminifera are 0 2 0 8 higher than those of living foraminifera our results show that this discrepancy is related to the stratification of the upper water mass and generally increases at low latitudes therefore as stratification of surface waters and seasonality depends on climatic conditions the relationship between temperature and 18o established on fossil foraminifera from recent sediment must be used with caution in paleoceanographic studies before models predicting seasonal flux abundance and 18o composition of a foraminiferal population in the sediment are available we recommend studying relative changes in isotopic composition of fossil planktonic foraminifera these changes primarily record variations in temperature and oxygen isotopic composition of sea water although part of the changes might reflect modifications of planktonic foraminifera seasonality or depth habitat

micron scale intrashell oxygen isotope variation in cultured planktic foraminifers abstract in this study we show that the rate of shell precipitation in the extant planktic foraminifer orbulina universa is sufficiently rapid that 12 h calcification periods in 18 o labeled seawater can be resolved and accurately measured using secondary ion mass spectrometry sims for in situ 18 o analyses calcifying o universa held at constant temperature 22 c were transferred every 12 h between ambient seawater 18 o w 0 4 vsmow and seawater with enriched barium and 18 o w 18 6 vsmow to produce geochemically distinct layers of calcite separated by calcite precipitated with an ambient geochemical signature we quantify the position of the ba labeled calcite in the shell wall of o universa via laser ablation icp ms depth profiling of trace element ratios and then measure intrashell 18 o calcite in the same shells using sims with a 3 m spot and an average precision of 0 6 2 sd measured 18 o calcite values in o universa shell layers are within 1 1 of predicted 18 o calcite values elemental and oxygen isotope data show that la icp ms and sims measurements can be cross correlated within the spatial resolution of the two analytical techniques and that 18 o calcite and elemental tracers appear to be precipitated synchronously with no measurable spatial offsets these results demonstrate the capability of sims to resolve daily growth increments in foraminifer shells and highlight its potential for paleoceanographic and biomineralization applications on microfossils

δ18o seasonality of planktonic foraminifera from southern ocean sediment traps latitudinal gradients and implications for paleoclimate reconstructions abstract the oxygen isotopic record obtained from globigerina bulloides globorotalia inflata and neogloboquadrina pachyderma s was analysed for 5 sediment traps moored in the southern ocean and southwest pacific the traps extend from subtropical to the polar frontal environments providing the first analysis of seasonal foraminiferal 18 o records from these latitudes comparison between the foraminiferal records and various equations for predicted 18 o of calcite reveals that the predicted 18 o is best captured by the equations of epstein et al 1953 epstein s buchsbaum r lowenstam h a urey h c 1953 revised carbonate water isotopic temperature scale geological society of america bulletin 64 1315 1326 and kim and o neil 1997 kim s t o neil j r 1997 equilibrium and non equilibrium oxygen isotope effects in synthetic carbonates geochimica et cosmochimica acta 61 3461 3475 the epstein equation shows a constant offset from the 18 o of g bulloides and n pachyderma s across the full range of latitudes the seasonal range in 18 o values for these two species implies a near surface habitat across all sites while g inflata most likely dwells at 50 m depth a significant finding in this study was that offsets from predicted 18 o for g bulloides do not correlate to changes in the carbonate ion concentration this suggests that co 3 2 in and of itself may not capture the full range of carbonate chemistry conditions in the marine system this sediment trap deployment also reveals distinct seasonal flux patterns for each species comparison between flux weighted isotopic values calculated from the sediment traps and the isotopic composition of nearby surface sediments indicates that the sedimentary records retain this seasonal imprint at the 51 s site g bulloides has a spring flux peak while n pachyderma s is dominated by summer production the imprint of these differing seasonal production patterns on the flux weighted 18 o values results in more depleted 18 o for n pachyderma s than for g bulloides interpretations of n pachyderma s isotopic composition as a record of subsurface conditions may therefore need to be refined with implications for interpretation of depleted glacial 13 c for this species sigman boyle 2000 sigman d m boyle e a 2000 glacial interglacial variations in atmospheric carbon dioxide nature 407 859 869

isrm suggested methods for land geophysics in rock engineering this paper presents seven suggested methods each suggested method is composed of seven section 1 general 2 applicability 3 planning 4 field operation 5 data processing 6 interpretation 7 output and report