variations in mode of formation and temperature of oceanic deep waters over the past 125 000 years marked changes in the deep water temperature of the different oceanic basins during the past 125 kyr are revealed by a detailed comparison of the oxygen isotopic composition ofbenthicforaminiferafrom sediment cores taken from the norwegian sea and the pacific atlantic and southern oceans the last interglacial deep water temperatures were similar to the modern ones at the 5e 5d transition around 115 kyr bp the deep water temperatures dropped below approximately 0 c in the pacific and southern indian oceans in the atlantic ocean the deep water temperature dropped in 2 successive steps at 115 and 75ky bp the global ocean deep water temperatures were in the 0 to 1 c range for the whole of the last ice age isotope stages 4 2

the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

could deep subantarctic convection feed the world deep basins during the last glacial maximum simple box model calculations are used to simulate the oceanic circulation during the last glacial maximum lgm these experiments show that the main features of the 13c and 14c distributions and of the lysocline depth may be explained by a circulation pattern very different from the modem one intermediate and upper deep waters were produced in the north atlantic ocean whereas deep waters of subantarctic mode type forming at the northern edge of the subantarctic convergence invaded the main oceanic basins the southern ocean mainly self ventilated had a reduced deep component that flew southward along the east pacific ridge and the australian west cost the thermodynamic fractionation that occurs during air sea exchange has only contributed slightly to the glacial deep 13c distribution through surface water temperature variations

changes in deep ocean water δ18o and temperature from the last glacial maximum to the present estimates are made of changes of the oxygen isotope anomaly of deep ocean water and of deep ocean temperature for the atlantic indian and pacific oceans from the time of the last glacial maximum to the present several independent sources of data including oxygen isotope records of planktic and benthic foraminifera at selected core sites primarily in the equatorial oceans climate long range investigation mapping and prediction sea surface temperatures estimates and geosecs 18o data for the present ocean water are utilized together with the paleotemperature equation of epstein et al 1953 glacial to interglacial change in oxygen isotope composition of the global deep ocean water is found to be 1 41 per mil compared with a global average change of 1 75 per mil for benthic foraminifera the former value implies a sea level change between 128 and 141 m depending on the choice of the isotope sea level conversion constant a global deep ocean warming of 1 4 c from glacial maximum to the present is found from the above isotopic difference of 0 34 per mil the consistency of the results in this paper with those of chappell and shackleton 1986 suggest that there is no significant contribution from isotopically light floating ice shelves surrounding antarctica as proposed by johnson and andrews 1986 at least for the change from glacial maximum to the present the ocean transition from glacial to interglacial episodes was accompanied by an estimated warming of 2 0 c in the atlantic 1 4 c in the indian and 1 1 c in the pacific oceans the glacial pacific was colder than the atlantic ocean but the difference between the two oceans was smaller than today

cd ca changes in a deep cape basin core over the past 730 000 years response of circumpolar deepwater variability to northern hemisphere ice sheet melting a comparison of cadmium calcium cd ca records of benthic foraminifera from a deep cape basin and a deep eastern equatorial pacific core suggests that over the past 400 000 years the nutrient concentration of circumpolar deep water cpdw has always been lower than that of the deep pacific the data further suggest that at the 100 000 and 23 000 year orbital periods the contribution of north atlantic deep water to cpdw is at a maximum during periods of ice growth and at a minimum during periods of ice decay these results are not in agreement with results based on carbon isotope records of benthic foraminifera which suggest intervals of cpdw nutrient enrichment relative to the deep pacific and an approximately in phase relationship between cpdw nutrient concentration and ice volume resolution of the apparent conflict between 13c and cd ca data may provide important constraints on past deep ocean circulation and nutrient variability

new unspiked k ar ages of volcanic rocks of the central and western sector of the aeolian islands reconstruction of the volcanic stages abstract a geochronological study of the filicudi salina lipari and vulcano islands aeolian archipelago using the unspiked potassium argon technique provides new age data which combined with stratigraphic correlation better constrain the temporal evolution of volcanism the unspiked k ar age of the oldest exposed lavas on filicudi 219 5 ka is significantly younger than the previous estimation of 1 02 ma in the general context of aeolian volcanism this new date suggests that the volcanism of the western sector of the aeolian archipelago is younger than previously thought geochronological data point out on the rapid transition from calc alkaline to potassic volcanism the distribution of the k ar ages within the salina lipari vulcano group shows that the volcanism started on lipari and propagated over time northward on salina and southward on vulcano geochronological and geophysical data suggest that the onset of volcanism in the central sector of the aeolian arc may be due to a mantle upwelling structure located below lipari a change in the style of the eruptions occurred in the salina lipari vulcano system at about 100 ka from the present low energy magmatic eruptions occurred between 188 and about 100 ka from about 100 ka to the present higher energy eruptions and low energy events due to magma water interaction also occurred this change in the style of activity together with the appearance of evolved products i e rhyolites during the last 50 ka is consistent with the formation of magmatic reservoirs located at shallower depth with respect to those of the 188 100 ka period the new geochronological data and available petrological models reveal that a change in the deep source of the primary magmas occurred in a relatively short time interval

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

calcitic foraminiferal data confirmed by cadmium in aragonitic hoeglundina application to the last glacial maximum in the northern indian ocean a core top study of cadmium uptake into the shells of the aragonitic benthic foraminifera hoeglundina elegans demonstrates that the hoeglundina cd ca partition coefficient is close to 1 0 throughout the ocean cd uptake by hoeglundina is far less depth dependent than that of calcitic benthic foraminifera furthermore manganese carbonate does not precipitate on these aragonitic shells allowing for the recovery of cd estimates in some samples where calcitic species are spoiled by contaminating overgrowths because cd incorporation into hoeglundina shows little depth dependence a comparison of calcitic and hoeglundina cd data can be used to verify the assumption that the depth dependence observed for calcitic benthic foraminifera is time invariant this comparison has been undertaken in downcore and last glacial maximum lgm samples from the northern indian ocean aragonitic and calcitic foraminiferal estimates for cd in the lgm ocean are in excellent agreement this result indicates upper ocean estimates of lgm cd are reliable despite a factor of two variation in cd uptake by calcitic species over this depth range cd and 13c data indicate that the uppermost waters of the lgm arabian sea were strongly nutrient depleted relative to today but that the deepest waters of the northern bay of bengal had nutrient concentrations at least as high as or higher than modern levels a strong vertical gradient of increasing nutrients with increasing depth existed in both basins during the lgm a west to east gradient of increasing nutrient concentrations also is evident at all depths in the bay of bengal there is evidence for an enhanced gradient of nutrients increasing from south to north the lgm deep arabian sea and intermediate depth bay of bengal were nutrient depleted compared to the modern ocean however cd and 13c data indicate that nutrient depletion in the northern indian ocean did not exceed that of the deep eastern tropical pacific except during the latest part of oxygen isotope stage 2 and according to cd data only the early stages of deglaciation during oxygen isotope stage 3 and early stage 2 cd in the northern indian ocean and cd in the eastern tropical pacific were indistinguishable although both regions have lower cd at these times compared to the holocene

kinematic significance of mingling rolling structures in lava flows a case study from porri volcano salina southern tyrrhenian sea a basaltic andesite lava flow from porri volcano salina southern tyrrhenian sea is composed of two different magmas magma a 51 vol of crystals has a dacitic glass composition and magma b 18 vol of crystals a basaltic glass composition magma b is hosted in a and consists of sub spherical enclaves and boudin like banding and rolling structures rs four types of rs have been recognized type type complex types and transitional structures between sub spherical enclaves and rolling structures an analysis of the rs has been performed in order to reconstruct the flow kinematics and the mechanism of flow emplacement rolling structures have been selected in three sites located at different distances from the vent in all sites most rs show the same sense of shear kinematic analysis of rs allows the degree of flow non coaxiality to be determined the non coaxiality is expressed by the kinematic vorticity number wk a measure of the ratio sr between pure shear strain rate and simple shear strain rate the values of wk calculated from the measured shapes of microscopic rs increase with increasing distance from the vent from approximately 0 5 to 0 9 results of the structural analysis reveal that the rs formed during the early intermediate stage of flow emplacement they represent originally sub spherical enclaves deformed at low shear strain at higher strain rs deformed to give boudin like and stretched banding structures results of the kinematic analysis suggest that high viscosity lava flows are heterogeneous non ideal shear flows in which the degree of non coaxiality increases with the distance from the vent in the vent area deformation is intermediate between simple shear and pure shear farther from the vent deformation approaches ideal simple shear lateral extension processes occur only in the near vent zone where they develop in response to the lateral push of magma extruded from the vent lateral shortening processes develop in the distal zone and record the gravity driven movement of the lava the lava flow advanced by two main mechanisms lateral translation and rolling motion lateral translation equals rolling near the vent while rolling motion prevailed in the distal zones

depth profiles of δ13c in bottom water and core top c wuellerstorfi on the ontong java plateau and emperor seamounts we have measured the carbon isotopic composition of dissolved inorganic carbon in bottom waters of the ontong java plateau western equatorial pacific and on the northern emperor seamounts northwest pacific each of these locations is several hundred miles from the nearest geochemical ocean sections study geosecs stations and the observed 13c values at each site differ substantially from regionally averaged geosecs 13c profiles we discuss the possible causes of these differences including horizontal variability near bottom effects and problems with the pacific geosecs 13c data we also measured the isotopic composition c and o of core top c wuellerstorfi from a depth transect of cores at each location the 18o data are used to verify that our samples are holocene comparison of foraminiferal and bottom water 13c values shows that this species faithfully records bottom water 13c at both sites and demonstrates that there is no depth related artifact in the dissolved inorganic carbon c wuellerstorfi 13c relationship at these sites

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

oxygen isotopes and sea level from the time that detailed oxygen isotope records derived from foraminifera living in the constant temperature environment of the abyssal ocean became available there has been a discrepancy between the ice volume record that these records imply and that derived from the altitude of dated coral terraces around the world here we re examine the data and conclude that the temperature of the abyssal ocean has been an actively varying component of the climate system

old radiocarbon ages in the southwest pacific ocean during the last glacial period and deglaciation marine radiocarbon 14c dates are widely used for dating oceanic events and as tracers of ocean circulation essential components for understanding ocean climate interactions past ocean ventilation rates have been determined by the difference between radiocarbon ages of deep water and surface water reservoirs but the apparent age of surface waters currently approximately 400 years in the tropics and approximately 1 200 years in antarctic waters might not be constant through time as has been assumed in radiocarbon chronologies and palaeoclimate studies here we present independent estimates of surface water and deep water reservoir ages in the new zealand region since the last glacial period using volcanic ejecta tephras deposited in both marine and terrestrial sediments as stratigraphic markers compared to present day values surface reservoir ages from 11 900 14c years ago were twice as large 800 years and during glacial times were five times as large 2 000 years contradicting the assumption of constant surface age furthermore the ages of glacial deep water reservoirs were much older 3 000 5 000 years the increase in surface to deep water age differences in the glacial southern ocean suggests that there was decreased ocean ventilation during this period

enclaves provide new insights on the dynamics of magma mingling a case study from salina island southern tyrrhenian sea italy abstract three lava flows hereafter flows a b and c from salina island italy consist of basaltic andesitic enclaves dispersed in a dacitic matrix enclaves represent 8 12 vol of the erupted magma the number of enclaves and the surface covered by the enclaves at each outcrop do not vary significantly with the distance from the vent in the flows a and b these feature reflect the dynamics of magma mingling within the reservoir and not the kinematics of the lava flow in the flow c these parameters vary irregularly the statistical entropy s t of the enclaves which is a measure of their spatial distribution dispersion is estimated in outcrops located at different distance from the vent the kolmogorov sinai entropy rate k which describes the variations of s t with time is also determined in the lava flow a s t increases linearly with time t for 0 0 5 s t attains its maximum value and maintains constant with increasing t in the lava flow b s t linearly increases with t and k is 0 01 in the lava flow c there is not correlation between s t and t the comparison between the results from the analysis of the porri enclaves and those from numerical experiments on the variation of s t in chaotic advective mixing systems and from previous experimental models on magma mixing allow us to draw some conclusions on dynamics of the basaltic andesite dacite mingling in the magma chamber fully chaotic magma mingling systems show three evolution stages an initial stage which is unknown because of the disruption of the initial configuration of the interacting magmas a second stage characterized by a linear increase of the statistical entropy with time and a third stage in which the uniformity of the system is reached and the entropy does not vary with increasing time a system in which the uniformity is never attained is characterized by irregular variations of s t with time in the flows a and b the relations between s t and t are consistent with those of a fully chaotic dynamics possibly associated to convection the basaltic andesite was uniformly distributed in the dacitic host due to the occurrence of convective movements driven by the injection of the basaltic andesite within the dacitic chamber the mingling system recorded by the lava flow a evolved with a higher rate with respect to that of the flow b this suggests that chaotic advection stirring and folding is more efficient in the magmatic system a than in b on the contrary the mingling system c is characterized by a non uniform distribution of the basaltic andesite within dacite this reflects the occurrence of a dynamics in which stirring and folding processes do not operate efficiently and are unable to uniformly distribute the dispersed phase within the continuous one the decrease of k from a to b and the lack of a measurable k in c along with the observation that a and b were emitted before c indicate that the efficiency of advective movements within the porri magma chamber declined with decreasing time mingled magmas characterized by a homogeneous spatial distribution of enclaves or an initially inhomogeneous distribution evolving towards a homogeneous one are indicative of efficient advection processes that may favor magma mixing mingled magmas characterized by an inhomogeneous distribution of enclaves suggest low dynamical interaction between the two end members magma mixing is not allowed

relationships between deformation and mixing processes in lava flows a case study from salina aeolian islands tyrrhenian sea the massive unit of a lava flow from porri volcano salina aeolian islands displays many unusual structures related to the physical interaction between two different magmas the magma a represents approximately 80 of the exposed lava surface it has a crystal content of 51 vol and a dacitic glass composition sio2 63 64 wt the magma b has a basaltic andesite glass composition sio2 54 55 wt and a crystal content of approximately 18 vol it occurs as pillow like enclaves banding boudin like and rolling structures which are hosted in magma a structural analysis suggests that banding and boudin like structures are the result of the deformation of enclaves at different shear strain the linear correlation between strain and stratigraphic height of the measured elements indicates a single mode of deformation we deduce that the component b deformed according to a simple shear model glass analyses of the a b boundary indicate that a and b liquids mix together at high shear strain whereas only mingling occurs at low shear strain this suggests that the amount of deformation i e forced convection plays an important role in the formation of hybrid magmas high shear strain may induce stretching shearing and rolling of fluids which promote both forced convection and dynamical diffusion processes these processes allow mixing of magmas with large differences in their physical properties

glacial interglacial modulation of the marine nitrogen cycle by high latitude o2 supply to the global thermocline 1 an analysis of sedimentary nitrogen isotope records compiled from widely distributed marine environments emphasizes the global synchrony of denitrification changes and provides evidence for a strong temporal coupling of these variations to changes in nitrogen fixation as previously inferred we explain the global coherence of these records by a simple physical control on the flux of dissolved oxygen to suboxic zones and the coupling to fixation via the supply of phosphorus to diazotrophs in suitable environments according to our hypothesis lower glacial stage sea surface temperature increased oxygen solubility while stronger winds in high latitude regions enhanced the rate of thermocline ventilation the resultant colder rapidly flushed thermocline lessened the spatial extent of denitrification and consequently n fixation during warm periods sluggish circulation of warmer less oxygen rich thermocline waters caused expansion of denitrification zones and a concomitant increase in n fixation local fluctuations in export productivity would have modulated this global signal

non linear deformation and break up of enclaves in a rhyolitic magma a case study from lipari island southern italy 1 a dome from lipari island southern italy consists of 12 vol of circular elongated and folded latitic enclaves hosted in a rhyolitic matrix the dm to cm scale enclaves are more deformed than the mm scale blobs the critical value of the ratio between the viscous forces which allow deformation and eventually break up blobs of latitic magma and the interfacial tension forces is larger than 0 29 the reynolds number is 5 3 the equivalent radius and the axial ratio of the enclaves follow power law distributions this feature suggests that the break up and stretching of magmas are non linear scale invariant probably cyclic processes the coexistence of enclaves of different shape and the self similar size distributions suggest that chaotic advection plays a major role in the formation of mingled magmas caution must be used when measuring the finite strain from enclave shapes because they may break apart during the deformation

interocean exchange of glacial north atlantic intermediate water evidence from subantarctic cd ca and carbon isotope measurements new measurements of cd ca ratios for glacial benthic foraminifera from the continental shelf and slope off tasmania and south australia are presented when combined with glacial carbon isotope measurements lynch stieglitz et al 1994 these data from the glacial subantarctic zone suggest that a water mass with a high value of the conservative tracer 13cas occupied not only the shallow 1 2 km portions of the atlantic and pacific oceans but was present in the glacial subantarctic as well the oceanic cd concentrations cdw predicted for the glacial subantarctic are intermediate between those from the glacial atlantic and the glacial pacific supporting the idea that glacial north atlantic intermediate water may have reached the intermediate depth pacific via the antarctic circumpolar circulation lynch stieglitz and fairbanks 1994

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

a trace metal perspective on the evolution of antarctic circumpolar deep water chemistry a new benthic foraminiferal ba ca and cd ca data set from core rc13 229 in the deep cape basin indicates only small variations in bottom water nutrient concentrations in circumpolar deep water cpdw over the last 450 kyr variability in the ba record is characterized by somewhat higher values during glacial periods consistent with a reduction in the flux of ba depleted north atlantic deep water to the southern ocean during glacial periods the small changes in the ba and cd records contrast with the large and systematic increase in cpdw nutrients during glacial periods implied by the benthic 13c record this discrepancy essentially an extension of the well known southern ocean cd 13c conflict is evaluated by transforming rc13 229 paleochemical data into carbonate parameters using the modern oceanic relationships between 13c cd and co2 and between ba and alkalinity calculations using cd ca to estimate past variations in cpdw co2 and ba ca to estimate past variations in cpdw alkalinity yield carbonate ion concentrations that exceed calcite saturation throughout the record length with generally higher carbonate ion values associated with glacial intervals opposite in sense to the rc13 229 caco3 record substituting 13c to estimate co2 leads to extreme calcite undersaturation at this site during glacial periods clearly inconsistent with the preservation of calcite throughout the length of rc13 229 accepting the carbon isotope record as a direct measure of past variations in cpdw co2 concentrations requires that both the cd and ba evidence for limited nutrient and alkalinity changes be disregarded

aeromagnetic anomalies reveal hidden tectonic and volcanic structures in the central sector of the aeolian islands southern tyrrhenian sea italy 1 salina island italy in the central aeolian chain is the northernmost volcanic structure of an elongated ridge on a regional shear zone with nnw sse strike slip faults and second order n s and ne sw faults modeling of high resolution low altitude aeromagnetic data collected in 2003 and 2005 using volcanological data constraints reveals the inner structure of the salina volcanoes and surrounding marine regions regional negative anomalies overlie e w elongated sedimentary basins related to the early pliocene pleistocene opening of the southern tyrrhenian sea these negative anomalies flank positively magnetized crust of salina and seamounts off its eastern coast where the shorter wavelength anomalies map late pleistocene holocene volcanic conduits dikes and faults the magnetic and volcanological data indicate that the early circa 168 100 ka basaltic to andesitic salina volcanism developed along n s and ne sw tectonic faults whereas the more recent andesitic lavas and rhyolitic pyroclastics circa 100 13 ka were emitted by vents related to the main nw se faults the tectonic structures also controlled the location of the seamounts around the island and the geometry of the volcano tectonic collapses salina volcanism was emplaced on a nnw sse tear fault of the presently developing roll back slab in the southern tyrrhenian sea

high resolution stratigraphy in late pleistocene holocene sediments of the vema channel abstract twenty five giant gravity cores ggc were obtained from the southwest flank of the rio grande rise in the summer of 1980 and were analyzed for time slice interpretations of the late pleistocene paleoceanography of the southwestern atlantic the cores span a depth interval of 1430 4148 m encompassing each of the principal deep water masses the suite of cores contains a continuous depositional record of the past 150 000 200 000 years from calcium carbonate oxygen isotope carbon 14 and biostratigraphic analyses it is possible to determine the precision in core to core correlation which is obtainable within this region of relatively low accumulation rates 0 5 2 0 cm 10 3 yrs calcium carbonate analyses were performed on each of the 25 cores at 1 cm sampling intervals using a technique that yields an analytical precision of 0 25 the carbonate curves show glacial interglacial amplitudes of typically 10 30 caco3 higher frequency amplitudes of 2 5 are also present both the glacial interglacial and the higher frequency carbonate signals can be correlated from core to core over the entire depth interval of the transect and are essentially synchronous based on independent stratigraphic control provided in selected cores by 18o 14c and biostratigraphic analyses despite the low sedimentation rates within this particular region we obtain a precision in core to core correlation of 1000 2000 yrs over the late pleistocene holocene these high resolution studies from the vema channel have important implications for interpreting the effects of bioturbation on a given stratigraphic sequence modeling the effects of bioturbation on the abundance and isotopic records of the benthonic foraminifera planulina wuellerstorfi suggests that for the region of the vema channel rio grande rise invalid stratigraphic and paleoceanographic interpretations may result if abundance variations in this species are ignored the results of these analyses show that it is possible to generate detailed stratigraphies in regions that have not previously been selected for high resolution studies solely because of relatively low accumulation rates of sediments our results indicate that carbonate analyses in some regions may provide a distinct advantage over 18o analyses because of the ease of analysis and high precision for identifying low amplitude high frequency fluctuations which can be correlated from core to core at the same time independent stratigraphic control via 18o or 14c is essential to verify whether this technique of carbonate curve matching is valid

13c record of benthic foraminifera in the last interglacial ocean implications for the carbon cycle and the global deep water circulation the 13c 12c ratios of upper holocene benthic foraminiferal tests genera cibicides and uvigerina of deep sea cores from the various world ocean basins have been compared with those of the modern total carbon dioxide tco2 measured during the geosecs program the 13c difference between benthic foraminifera and tco2 is 0 07 0 04 for cibicides and 0 83 0 07 for uvigerina at the 95 confidence level 13c analyses of the benthic foraminifera that lived during the last interglaciation isotopic substage 5e about 120 000 yr ago show that the bulk of the tco2 in the world ocean had a 13c value 0 15 0 12 lower than the modern one at the 95 confidence level reflecting a depletion compared to the present value of the global organic carbon reservoir regional differences in 13c between the various oceanic basins are explained by a pattern of deep water circulation different from the modern one the antarctic bottom water production was higher than today during the last interglaciation but the eastward transport in the circumpolar deep water was lower

magma mixing by convective entrainment recent studies of volcanic eruptions have brought to light a puzzling sequence the ejection of dense and mixed liquids followed by a larger volume of unmixed less dense liquid1 4 although these studies have shown that the mixing is associated with the injection of basaltic liquid into a more silicic magma chamber a paradox remains basaltic magma is denser than silicic magma and should flow along the floor of the magma chamber this configuration impedes mixing of the two liquids and appears incompatible with the early eruption of basaltic liquid from the top of the chamber previously proposed mixing processes explain neither the eruption sequence nor the eruption of dense liquid during the time of lowest eruption rate1 8 we report here fluid mechanical experiments that suggest a solution a thermal plume forms over the replenishment inlet dragging basaltic liquid upward by viscous coupling and producing mixing only in a localized area without affecting the bulk of the chamber

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

changes in the mode of southern ocean circulation over the last glacial cycle revealed by foraminiferal stable isotopic variability benthic foraminiferal oxygen and carbon isotopic records from southern ocean sediment cores show that during the last glacial period the south atlantic sector of the deep southern ocean filled to roughly 2500 m with water uniformly low in 13c resulting in the appearance of a strong mid depth nutricline similar to those observed in glacial northern oceans concomitantly deep water isotopic gradients developed between the pacific and atlantic sectors of the southern ocean the 13c of benthic foraminifera in pacific sediments remained significantly higher than those in the atlantic during the glacial episode these two observations help to define the extent of what has become known as the southern ocean low 13c problem one explanation for this glacial distribution of 13c calls upon surface productivity overprints or changes in the microhabitat of benthic foraminifera to lower glacial age 13c values we show here however that glacial interglacial 13c shifts are similarly large everywhere in the deep south atlantic regardless of productivity regime or sedimentary environment furthermore the degree of isotopic decoupling between the atlantic and pacific basins is proportional to the magnitude of 13c change in the atlantic on all time scales thus we conclude that the profoundly altered distribution of 13c in the glacial southern ocean is most likely the result of deep ocean circulation changes while the characteristics of the southern ocean 13c records clearly point to reduced north atlantic deep water input during glacial periods the basinal differences suggest that the mode of southern ocean deep water formation must have been altered as well

a deeper respired carbon pool in the glacial equatorial pacific ocean article i nfo atmospheric pco2 was approximately 80 ppm lower during the last glacial period than during pre industrial times identifying the fate of that carbon has been one of the great challenges in paleoceanography we present evidence from ten equatorial pacific ocean sediment cores to show that the deep pacific ocean likely stored more carbon during the last glacial period than the holocene the concentration of the redox sensitive metal uranium u in sediments was systematically greater during the last glacial period than during the holocene indicating more reducing conditions in glacial age sediments reconstructions of biogenic opal flux indicate that changes in u distribution were not the result of changes in biological productivity and the ensuing rain of organic carbon to the sea floor which also affects the redox conditions of the sediments together these results lead to the interpretation that bottom water in the equatorial pacific during the glacial period had significantly lower oxygen concentration than during the holocene and a correspondingly greater level of respired co2 this conclusion is supported by evidence for greater preservation of brassicasterol a biomarker produced by diatoms in glacial age sediments of the eastern equatorial pacific the presence of additional respired co2 in the glacial deep ocean would have lowered atmospheric pco2 by 1 increasing the total storage of co2 in the glacial ocean and 2 increasing ocean alkalinity following a transient carbonate dissolution event our results are consistent with recently published data from the north pacific ocean this suggests that increased carbon storage in the glacial deep pacific ocean was a basin wide phenomenon consistent with a large scale transfer of carbon to the deep ocean during glacial periods

elemental and sr nd isotope geochemistry of microgranular enclaves from peralkaline a type granitic plutons of the emeishan large igneous province sw china abstract microgranular enclaves are common within intermediate to felsic granitic rocks that have i and s type affinity however they are rare within alkaline anorogenic granitoids of a type affinity the permian 260 ma emeishan large igneous province elip of southwest china contains two peralkaline silica saturated a type granitic plutons that host microgranular enclaves the enclaves from the baima pluton are intermediate in composition and have lower sio 2 and higher tio 2 cao and mg sio 2 57 2 to 63 0 wt tio 2 0 8 to 1 8 wt cao 1 7 to 3 3 wt mg 28 to 44 than their host sio 2 62 6 to 67 8 wt tio 2 0 5 to 1 4 wt cao 0 4 to 1 8 wt mg 15 to 31 the enclaves from the taihe pluton are more felsic sio 2 63 8 to 71 3 wt tio 2 0 3 to 0 6 wt cao 0 6 to 2 3 wt mg 8 to 22 but are still less evolved than their host sio 2 69 8 to 75 1 wt tio 2 0 2 to 0 6 wt cao 0 4 to 0 8 wt mg 3 to 12 in both cases the enclaves have very similar end t values baima end t 2 8 to 3 2 taihe end t 1 0 to 2 0 as their hosts baima end t 3 0 to 3 2 taihe end t 1 5 to 1 9 the major and trace element trends of the enclave host pairs suggest that fractional crystallization occurred and that element diffusion was likely minimal the enclaves are interpreted as entrained accumulations of early formed crystals of a silicic magma which was originally produced by fractional crystallization of a mafic magma

glacial interglacial changes in water mass structure and flow in the sw pacific ocean eight to ten point depth profiles from 1200 to 4800 m water depth of oxygen and carbon isotopic values derived from benthic foraminifera averaged over selected times in the past 160 ka are presented the data are from 10 sediment cores off eastern new zealand mainly north chatham rise this lies under the deep western boundary current in the southwest pacific and is the main point of entry for several water masses into the pacific ocean the benthic isotopic profiles are related to the structure of water masses at present and inferred for the past these have retained a constant structure of lower circumpolar deep water upper circumpolar deep water north pacific deep water antarctic intermediate water with no apparent changes in the depths of water mass boundaries between glacial and interglacial states sortable silt particle size data for four cores are also examined to show that the vigour of the inflow to the pacific while variable appears to have remained fairly constant on average among the lowest last glacial maximum values of benthic 13c in the world ocean 1 03 based on cibicidoides wullerstorfi occurs here at 2200 m comparable values occur in the atlantic sector of the southern ocean while those from the rest of the pacific are distinctly higher confirming that the southern ocean was the source for the unventilated nutrient enriched water seen here oxygen and carbon isotopic data are compatible with a glacial cold deep water mass of high salinity but lower nutrient content or better ventilated below 3500 m depth this contrasts with the south atlantic where unventilated nutrient enriched water extends all the way to the sea bed comparison with previous studies also suggests that the deeper reaches of the antarctic circumpolar current below 3500 m are not homogeneous all around the southern ocean with the kerguelen plateau and or the macquarie balleny ridges posing barriers to the eastward spread of the deepest low 13c water out of the south atlantic in glacials these barriers combined with inferred high density of bottom waters restricted inter basin exchange and allow three glacial domains dominated by bottom waters from weddell sea adelie coast and ross sea to be defined we suggest that the ross sea was the main source of the deep water entering the pacific below 3500 m

carbon 13 in pacific deep and intermediate waters 0 370 ka implications for ocean circulation and pleistocene co2 stable isotopes in benthic foraminifera from pacific sediments are used to assess hypotheses of systematic shifts in the depth distribution of oceanic nutrients and carbon during the ice ages the carbon isotope differences between 1400 and 3200 m depth in the eastern pacific are consistently greater in glacial than interglacial maxima over the last 370 kyr this phenomenon of bottom heavy glacial nutrient distributions which boyle proposed as a cause of pleistocene co2 change occurs primarily in the 1 100 and 1 41 kyr 1 milankovitch orbital frequency bands but appears to lack a coherent 1 23 kyr 1 band related to orbital precession averaged over oxygen isotope stages glacial 13c gradients from 1400 to 3200 m depth are 0 1 greater than interglacial gradients the range of extreme shifts is somewhat larger 0 2 to 0 5 in both cases these changes in pacific 13c distributions are much smaller than observed in shorter records from the north atlantic this may be too small to be a dominant cause of atmospheric pco2 change unless current models underestimate the sensitivity of pco2 to nutrient redistributions this dampening of pacific relative to atlantic 13c depth gradient favors a north atlantic origin of the phenomenon although local variations of pacific intermediate water masses can not be excluded at present

the strain path and emplacement mechanism of lava flows an example from salina southern tyrrhenian sea italy abstract a lava flow from salina southern tyrrhenian sea consists of subcircular to ellipsoidal basaltic enclaves dispersed in a dacitic host a 2d strain and kinematic analysis of the enclaves has been performed in order to determine a the relative contribution of the coaxial and non coaxial components to the bulk flow deformation b the flow vorticity wk c the strain path and d the mechanism of flow emplacement the axial ratio r f and the angle f between the long axis of the enclaves and the transport direction have been measured in 196 sites located at different distances from the vent in the near vent zone whereas further from the vent values were always larger than 1 ranging from 1 6 in the near vent zone to 1 at the front values were between 0 2 at the back and 2 6 at the front wk was between 0 13 and 1 and increased from the back to the front the enclaves result from the injection of basalt into dacite most of the deformation was acquired during the lava flow emplacement and not during the rise in the conduit plug flow the strain path depicted by the enclaves is consistent with that resulting from experimental analogue models and reveals that the lava suffers lateral extension near the vent further from the vent the lava deforms according to an ideal non coaxial model the lava emplacement is mainly controlled by the gravity evidence of deformation induced by the magma pressure is lacking near the vent the lava behaves as a hyperbolic flow whereas at the front it behaves as a simple shear flow the mechanism of flow emplacement is consistent with a mixed viscous gliding spreading transport model at the back and with a viscous gliding model at the front

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

microgranitic enclave shapes and magmatic strain histories constraints from drop deformation theory microgranitic mafic enclaves are common components of plutonic bodies and may represent the result of mingling of mafic and felsic magmas these enclaves are often ellipsoidal or elongate in shape in order to constrain the conditions under which such enclaves were generated and deformed by their host pluton we apply drop deformation theory to model their distortion our model takes into account the change in viscosity of both the host and enclave with temperature composition and the amount of suspended solids in enclave host systems and it assumes that simple shear flow predominates in the plutonic system we focus on the deformational history of enclaves over the time period in which they remain liquid and are either more or less viscous than their granitic host we find that the most stable enclaves with respect to being broken up by their entraining flow are generally the most mafic enclaves those with silica contents near those of the host granite are highly unstable this is in reasonable accord with field observations of the abundance of enclaves of different chemistry most deformation of microgranitic enclaves is likely to occur at relatively high temperatures probably between 950 c and 1050 c and therefore the enclaves record magmatic strain of the host over only a limited temperature time range in the host s cooling history furthermore the observation of apparent deformation of these enclaves in a liquid regime coupled with our calculated dependences of enclave deformation on flow velocity implies that magmatic flow velocities are likely to be below 10 m yr in enclave bearing plutonic systems

the dimensions of magmatic inclusions as a constraint on the physical mechanism of mixing abstract silicic lavas often bear inclusions of more mafic lava several physical processes have been proposed by which these magmas may become mixed measurements of the sizes of mafic inclusions in lavas of two calc alkaline volcanoes are used here to obtain a characteristic length scale for this type of mixing and provide a means to discriminate between different mixing processes we quantitatively assess the proposal that in a stratified reservoir dynamic interactions of rising gas bubbles with the interface between a lower layer of mafic magma and an upper layer of silicic magma lead to the formation of vesiculated blobs of the lower magma in the upper one this is due to gravitational instability of a foam layer growing at the interface between the two magmas our theoretical calculations of this instability predict both the correct order of magnitude for the characteristic size of inclusions and the way in which inclusion size varies with the physical properties of the magmas this fluid dynamic framework is used to map out different possible flow regimes and place constraints on the fraction of gas in these systems

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

glacial to interglacial changes in surface nitrate utilization in the indian sector of the southern ocean as recorded by sediment δ15n we present a new approach for paleoceanographic reconstruction of surface nutrient utilization in the southern ocean it has been observed in the contemporary ocean that due to preferential uptake of 14no3 during photosynthesis the 15n of planktonic organic matter increases with increasing nitrate depletion in surface waters our results demonstrate that the 15n signal produced in surface waters is reflected in the underlying surface sediments core top 15n is inversely correlated with surface nitrate concentration along a transect across the subtropical convergence and the polar front in the southeast indian ocean these results are consistent with a four box model showing that the nitrogen isotopic composition of sinking organic matter depends on percent nitrate utilization in the euphotic zone by comparing the 15n of surface sediments with that measured in the glacial sections of several cores we infer changes in the intensity and latitudinal distribution of nitrate uptake in this region during the last glacial maximum these preliminary results argue against increased biological uptake of nutrients in southern polar waters as a major mechanism for glacial lowering of atmospheric co2 they also suggest that subantarctic waters in the se indian sector became more nutrient depleted as they migrated northward increased nitrate depletion might have also occurred slightly south of the glacial polar front we use a six box model to explore the possible impact of this observation on atmospheric co2

burial of redox sensitive metals and organic matter in the equatorial indian ocean linked to precession authigenic metals uranium cadmium and molybdenum organic carbon oc and total c37 alkenone totc37 concentrations were measured for the last 350 kyr in core md900963 located in the eastern equatorial arabian sea authigenic metal concentrations on a carbonate free basis range between 1 and 17 ppm 0 5 and 6 ppm and 0 5 and 4 ppm for u cd and mo respectively the profiles are characterized by well defined 23 kyr cycles between oxic and mildly suboxic conditions the redox sensitive metal profiles also follow variations in the concentrations of oc 0 2 0 9 and alkenones 0 2 6 7 ppm the coupled variations in inorganic and organic constituents are attributed to a 23 kyr cycle in primary production above site md900963 as suggested by clear correlations with independent micropaleontologic proxies primary productivity indices based on foraminifera and coccoliths and fragmentation of foraminiferal shells the 23 kyr cycles do appear to be primarily driven by productivity rather than changes in bottom water oxygen comparison with other records indicates that if this interpretation is correct productivity variations across much of the indian ocean have been dominated by precessional forcing with high productivity in phase with low summer insolation in the northern hemisphere this interpretation contrasts with the traditional attribu tion of enhanced productivity in the indian ocean with periods of high summer insolation copyright 2002 elsevier science ltd

glacial and holocene stable isotope distributions in the southeastern indian ocean we have reconstructed glacial interglacial variations in cibicidoides wuellerstorfi 13c and 18o in the southeastern indian ocean using depth transects of cores from off western and southern australia we compare these new results with published stable isotope records to constrain glacial interglacial changes in indian ocean chemistry and circulation the strong last glacial maximum lgm deep water 13c depletions previously observed for the northeastern indian ocean did not extend throughout the low latitude glacial indian ocean we observe only a small lgm 13c decrease off southern australia in marked contrast to the strong lgm 13c depletions observed in many cores from the atlantic and western indian sectors of the southern ocean it is not yet clear whether the very low lgm 13c values in the deep northern and southwestern indian ocean are an artifact of surface ocean productivity or whether they reflect real gradients in deep water chemistry

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

evidence of crustal melting events below the island of salina aeolian arc southern italy quartz rich xenoliths hosted in the basaltic andesitic and andesitic lavas of monte dei porri in the island of salina contain fluid and melt inclusions whose study makes it possible to trace back the magma ascent path of this volcano moreover they are a source of information about the anatectic processes that occurred under this island the texture mineralogy and whole rock chemistry of these rocks exhibit the typical characteristics of a residual rock which went through several melt extraction events the chemistry of melt inclusions hosted inside quartz grains sio 2 72 7 al 2 o 3 9 0 13 5 cao 0 2 4 3 k 2 o 3 1 mgo feo t 1 5 supports the hypothesis that a progressive and continuous anatectic processes affected a peraluminous high grade metamorphic rock gneiss or micaschist that constituted the calabro peloritani basement and generated a quartz bearing residue the fluids trapped inside these inclusions are rarely composed of high density co 2 with a homogenization temperature to liquid phase th l within the range 26 2 31 0 c corresponding to densities of 520 to 690 kg m 3 more commonly they are made up of low density co 2 with a homogenization temperature to vapour phase th v within the range 13 2 31 0 c corresponding to density values of 150 to 460 kg m 3 it is proposed that during ascent batches of magma rising from the mantle sampled various fragments of a residual rock from a depleted metamorphic basal layer and carried them to the surface magmas probably stopped inside at least two distinct reservoirs located at different depths 12 7 km and between 1 7 and 4 7 km in which they underwent fractional crystallization the ascent speed of the xenolith bearing magmas from the deeper storage area to the shallower reservoir was fairly high as confirmed by the low number of high density fluid inclusions preserved that show re equilibration features and by the contemporaneous presence of denser cumulitic ol cpx opx xenoliths in the host lava

last glacial maximum paleochemistry and deepwater circulation in the southern ocean evidence from foraminiferal cadmium south atlantic benthic foraminiferal cd ca shows no glacial interglacial variation suggesting that the glacial contribution of north atlantic deep water to the southern ocean was not much different than at present in contrast cd ca in southeast indian ridge cores show lower glacial bottom water cd comparable to levels in intermediate depths of the north atlantic and significantly lower than in the deep south atlantic low glacial cd ca was also recorded in planktonic foraminifera suggesting a substantial decrease in the nutrient concentration of subantarctic surface water during the glacial maximum which most likely was caused by increased biological productivity the cd data are inconsistent with low glacial benthic foraminiferal 13c which suggest higher nutrient concentration we propose that the low cd ca in the southeast indian ridge records reflects a local source of nutrient depleted deepwater formed during the last glacial maximum by open ocean convection near the antarctic polar front downstream of the kerguelene plateau if this source was limited to the southeast indian basin then its impact on the overall chemistry of glacial circumpolar deepwater was rather small however if during glaciations open ocean convection became the dominant mode of bottom water formation it might have had a greater impact on cpdw chemistry

the accretion rate of extraterrestrial 3he based on oceanic 230th flux and the relation to os isotope variation over the past 200 000 years in an indian ocean core abstract in the eastern equatorial indian ocean the flux of extraterrestrial 3 he a proxy of interplanetary dust particles idps has been relatively constant over the past 200 ka the flux is equal to 1 1 0 4 10 12 cm 3 stp cm 2 ka 1 a value obtained using the xs 230 th profiling method variations in mass accumulation rates mars derived assuming a constant extraterrestrial 3 he flux have a 40 ka periodicity similar to that observed in the 18 o derived mars this frequency is similar to that of the earth s obliquity measured 187 os 188 os ratios are less radiogenic than present day seawater 0 49 0 98 reflecting the mixing of os derived from extraterrestrial terrigenous and hydrogenous sources when coupled with he data measured on the same samples os isotope data yield important information about the terrigenous component supplied to the eastern equatorial indian ocean the amount of os in the sample derived from the extraterrestrial component can be deduced with the help of the helium systematics once corrected for the extraterrestrial component of os os isotope signatures in conjunction with the 4 he concentrations suggest a supply of terrigenous material from indonesian ultramafic and himalayan crustal sources that clearly varies through time

chaotic dynamics and fractals in magmatic interaction processes a different approach to the interpretation of mafic microgranular enclaves abstract fractals have been used for describing a wide range of natural processes however applications of fractal geometry to the study of magma mingling mixing processes is almost completely lacking in spite of the fact that such an approach could give new insights into the nature of magmatic interactions fractal analyses of two geochemically linked groups of mafic microgranular enclaves mme from the sithonia plutonic complex northern greece have been performed because of the difficulties involved in using contours of enclaves to estimate their fractal dimensions a different approach is used in this paper fractal dimension is estimated using distribution maps of chemical elements inside enclaves the results obtained indicate that a clear correlation between fractal dimensions of enclaves and geochemical evidences of interaction exists and hence the two groups of enclaves reflect different degrees of interaction from a dynamical point of view stretching and folding processes between two magmas with different rheologies are considered representative of magmatic interaction this dynamic system can easily generate chaotic patterns recognized by the presence of fractal structures the contemporaneous occurrence of well mixed regions together with poorly mixed regions in the same system is thought to be similar to the host enclave system found in many granitoid plutons in particular mme are believed to represent islands of partially mixed mafic fluid subjected to different degrees of interaction with the host granitoid whereas host rocks are believed to represent mixed regions where the mixing process acted more efficiently producing almost completely hybrids it is shown that fractal geometry and chaotic dynamics can be considered suitable techniques in studying complex petrological phenomena and they can represent helpful methods in the development of petrogenetic models

paleoproductivity from benthic foraminifera abundance glacial to postglacial change in the west equatorial pacific surface productivity is correlated with the rate of accumulation of benthic foraminifera on the deep sea floor as a rule of thumb for each 1 mg of organic carbon arriving at the sea floor one benthic foram shell 150 m is deposited the correlation can be used to reconstruct organic flux to the sea floor in the past and hence the productivity of past oceans applying the appropriate equations to box core data from the ontong java plateau in the western equatorial pacific we found that productivity during the last glacial maximum exceeded present productivity by a factor of between 1 5 and 2 0 with intermediate values for the mid transition period accumulation of benthic foraminifera was depressed on top of the plateau during the glacial and transitional period presumably because increased winnowing removed part of the food supply

distant origin of circulation changes in the indian ocean during the last deglaciation abstract well dated benthic foraminifera isotopic records reveal that circulation changes repeatedly took place in the tropical indian ocean around 2000 m depth over the last deglaciation we show that the observed changes can be explained by large scale reorganization of intermediate water masses in the atlantic and indian oceans more specifically during heinrich event 1 and the younger dryas while the formation of north atlantic deep water was greatly reduced brine formation in the north atlantic and nordic seas led to the production of intermediate waters that extended far enough in the south atlantic to be deflected by the circumpolar currents into the indian ocean basin creating a circulation branch at intermediate depths that was more active than today in contrast during the last glacial maximum the bolling allerod and after the younger dryas there was no rapid transport of intermediate waters from the north atlantic to the south atlantic or indian ocean around 2000 m depth

similar glacial and holocene deep water circulation inferred from southeast pacific benthic foraminiferal carbon isotope composition we present holocene and last glacial maximum lgm oxygen and carbon isotope measurements on planulina wuellerstorfi in six southeast pacific cores sedimentation rates are low in this part of the ocean and measurements were made on individual foraminiferal shells in order to identify the holocene and glacial individuals on the basis of their extreme 18o the new 13c data were combined with previous p wuellerstorfi data for interpretation of global thermohaline circulation data from the southern ocean were examined closely for regional coherency and a few anomalous 13c values suspected of having productivity overprint were removed the resulting global 13c distributions and gradients indicate that the deep water circulation was similar during the holocene and lgm this interpretation brings 13c data to a better agreement with cd ca data and marks a sharp contrast with a widely held view based on 13c measurements that the glacial southern ocean was the terminus of the thermohaline circulation the proposed presence of glacial north atlantic deep water does not necessarily contradict the postulated presence of glacial north atlantic intermediate water

antarctic density stratification and the strength of the circumpolar current during the last glacial maximum the interaction between ocean circulation and biological processes in the southern ocean is thought to be a major control on atmospheric carbon dioxide content over glacial cycles a better understanding of stratification and circulation in the southern ocean during the last glacial maximum lgm provides information that will help us to assess these scenarios first we evaluate the link between southern ocean stratification and circulation states in a suite of climate model simulations while simulated antarctic circumpolar current acc transport varies widely 80 350 sverdrup sv it co varies with horizontal and vertical stratification and the formation of the southern deep water we then test the lgm simulations against available data from paleoceanographic proxies which can be used to assess the density stratification and acc transport south of australia the paleoceanographic data suggest a moderate increase in the southern ocean stratification and the acc strength during the lgm even with the relatively large uncertainty in the proxy based estimates extreme scenarios exhibited by some climate models with acc transports of greater than 250 sv and highly saline antarctic bottom water are highly unlikely

subarctic pacific evidence for a glacial deepening of the oceanic respired carbon pool abstract measurements of benthic foraminiferal cadmium calcium cd ca have indicated that the glacial interglacial change in deep north pacific phosphate po4 concentration was minimal which has been taken by some workers as a sign that the biological pump did not store more carbon in the deep glacial ocean here we present sedimentary redox sensitive trace metal records from ocean drilling program odp site 882 nw subarctic pacific water depth 3244 m to make inferences about changes in deep north pacific oxygenation and thus respired carbon storage over the past 150 000 yr these observations are complemented with biogenic barium and opal measurements as indicators for past organic carbon export to separate the influences of deep water oxygen concentration and sedimentary organic carbon respiration on the redox state of the sediment our results suggest that the deep subarctic pacific water mass was depleted in oxygen during glacial maxima though it was not anoxic we reconcile our results with the existing benthic foraminiferal cd ca by invoking a decrease in the fraction of the deep ocean nutrient inventory that was preformed rather than remineralized this change would have corresponded to an increase in the deep pacific storage of respired carbon which would have lowered atmospheric carbon dioxide co2 by sequestering co2 away from the atmosphere and by increasing ocean alkalinity through a transient dissolution event in the deep sea the magnitude of change in preformed nutrients suggested by the north pacific data would have accounted for a majority of the observed decrease in glacial atmospheric pco2

interior hydrography and circulation of the glacial pacific ocean abstract the deep water of the pacific ocean is a key component of the global climate system on the time scale of late pleistocene glaciation and deglaciation despite its importance the deep pacific during the last glacial maximum has received relatively little attention compared to the deep atlantic in part because the pacific poorly preserves carbonate sediments on the sea floor here we review the current state of knowledge of the deep hydrography and circulation of the glacial pacific by examining available nutrient proxy data including some new 13 c and 18 o data measured on benthic foraminifera planulina wuellerstorfi from the vicinity of japan available benthic 13 c and 18 o and radiocarbon data from the pacific support the presence of a deep hydrographic boundary at around 2000 m during the last glacial maximum paleoceanography 3 1988 343 paleoceanography 7 1992 273 paleoceanography 13 4 1998 323 the deep hydrographic divide in the glacial pacific is similar to what is inferred in the atlantic quaternary research 18 1982 218 paleoceanography 3 1988 317 paleoceanography 3 1988 343 annual reviews of earth planetary sciences 20 1992 245 science 259 1993 1148 the indian nature 333 1988 651 paleoceanography 13 1998 20 and the southern ocean paleoceanography 11 1996 191 suggesting that this is a global phenomenon during the glacial time the upper water mass has a distinctly enriched 13 c compared to the deeper water mass whose possible origins are discussed

kinematic significance of morphological structures generated by mixing of magmas a case study from salina island southern italy morphological features of mixing mingling structures of heterogeneous juveniles from the 13 ka old upper pollara eruption salina island southern italy are studied these heterogeneous rocks result from the mixing between an andesitic and a rhyolitic magma concentration patterns generated by magma mixing are analyzed on digital images and results have been compared with those obtained from numerical simulations of mixing processes coupling chaotic advection and chemical diffusion results show that the upper pollara rocks were produced by mixing 24 49 of andesite and 76 51 of rhyolite multifractal analysis of the mixing structures is performed and the mixing intensity i e the degree of interaction between the two end member magmas has been deduced from the analysis of the singularity spectrum results show that narrower is the multifractal spectrum the higher is the degree of homogenization of magmas reynolds number re during mixing has been estimated from the geometrical analysis of mixing structures by using experimentally defined relationships between shape parameters and re results show that re is between ca 500 and 7000 there is a positive correlation between the estimated initial percentage of mafic magma in the different analyzed samples and re in agreement with the observation that the higher is the percentage of the mafic lower viscosity magma the higher is the turbulence of the mixing system in addition our analysis reveals an unexpected inverse relationship between the calculated re and the degree of magma homogeneity suggesting that energy dissipation may have had a major role in the controlling mixing process because dissipation is inversely proportional to the mixing efficiency results suggest that mixing processes between the andesitic and rhyolitic magmas mainly developed in the conduit it is also suggested that mixing occurred in a shear layer type or pipe type flow

shape and microstructure of microgranitoid enclaves indicators of magma mingling and flow abstract at tarandore point 328 km south of sydney new south wales australia two tonalite phases are in contact with a gabbroic diorite all belonging to the moruya batholith lobate to crenulate contacts pillowing of the more mafic phase in the more felsic phase net veining of the more mafic phase by the more felsic local chilling of the more mafic phase against the more felsic and an abundance of rounded to elongate microgranitoid enclaves all suggest mingling of magmas at the site of emplacement therefore all phases were emplaced before the others solidified and an order of intrusion cannot be determined the variety of microgranitoid enclaves suggests that repeated magma mingling has occurred linear geochemical trends indicate either magma mixing or restite unmixing as a prime cause of variation in the members of the moruya suite of granitoids direct evidence of mixing is not present but evidence that the magmas were substantially liquid at the time of emplacement sugests that mixing is possible restite unmixing is unlikely to be the prime process because near minimum melts which would occur in all granitoid phases according to that model should mix easily rather than mingling in fact mingling has occurred between tonalite phases of very similar composition which would not be expected if the liquid parts of enclaves were minimum melts available experimental and theoretical data on mixing in both magma chambers and conduits cannot be applied directly to the occurrence at tarandore point owing to inadequately constrained parameters but mixing generally should be favoured by higher temperatures which is consistent with our inference that relatively high proportions of melt were present in the granitoid phases at the time of emplacement conduit mixing may be reflected in a local zone of strong to extreme elongation of enclaves in which the distortion has been accomplished by magmatic flow without solid state deformation as evidenced by strong dimensional preferred orientations coupled with a lack of microstructural evidence of intragranular plastic strain this suggests that elongate enclaves should not be used as indicators of solid state deformation or as tectonic strain markers without microstructural evidence that suitably strong intracrystalline plastic deformation has taken place

evidence for a bathyal front at 2000 m depth in the glacial pacific based on a depth transect on ontong java plateau data on oxygen and carbon isotope compositions of the benthic foraminifer planulina wullerstorfi from 18 cores 17 box cores and one piston core from ontong java plateau provide proxy depth profiles for temperature water mass and nutrient content for the late holocene the last transition and the last glacial the 18o profile during glacial time shows an increased gradient at a depth near 2000 m the corresponding 13c data suggest that a bathyal nutricline existed close to the same depth level the 13c values provide limits on the global change in carbon content of the glacial ocean which may be estimated as distinctly less than 1 atmospheric carbon mass 1 acm 700 gtc the greater co2 content of glacial deep waters which is reflected in the more negative 13c values may be at least in part due to a more sluggish renewal of abyssal deep waters if so the water of the deep pacific was up to 400 years older than now in turn ventilation in the upper waters above 2000 m may have been more vigorous than today

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

enhanced sedimentation along the equator in the western pacific measurements on cores from the ontong java plateau demonstrate that on equator sediment accumulates more 230th than is produced in the overlying water column in contrast cores from 3 8 n accumulate an amount of excess 230th more nearly equal to that produced in the overlying water column taken together with the observation that both the caco3 and non caco3 components of the sediment accumulate at approximately twice the rate in on equator than in off equator cores broecker et al 1999 this requires either that the rain of the larger amount of organic matter generated above the equatorial upwelling plume entrains excess clay and 230th during its fall to the sea floor or that physical transport processes either in the upper ocean or near the sea bed redistribute sediments in such a way that they preferentially accumulate in a narrow 1 latitude equatorial centered belt

glacial deep water geometry south atlantic benthic foraminiferal cd ca and δ13c evidence a depth transect of cores from 1268 to 3909 m water depth in the western south atlantic are ideally situated to monitor the interocean exchange of deep water and variations in the relative strength of northern and southern sources of deep water production benthic foraminiferal cd ca and 13c data suggest that glacial north atlantic intermediate water gnaiw extended at least as far south as 28 s in the western south atlantic the core of nutrient depleted water was situated at 1500 m above and below water masses with higher nutrient concentrations when examined in conjunction with published paired cd ca and 13c from intermediate depth cores from other basins it appears that the extent of gnaiw influence on the intermediate waters of the world s oceans was less than suggested previously differentiating among possible pathways for the glacial deep ocean 3 km requires a better understanding of the controls on cd ca and 13c values of benthic foraminifera

deformation patterns in a high viscosity lava flow inferred from the crystal preferred orientation and imbrication structures an example from salina aeolian islands southern tyrrhenian sea italy shape preferred orientation and imbrication structures of crystals have been measured on samples representative of the base centre and top of a highly viscous lava flow on salina aeolian islands southern tyrrhenian sea the data allow zones with different deformation patterns to be identified in the base and top of the flow deformation leads to the development of discrete preferred orientation and imbrication of the elongate crystals the sense of shear is right lateral at the base and left lateral at the top of the flow shear strain can be estimated by the analysis of crystal preferred orientation deformation increases from the flow centre to the outer more viscous boundary layers random orientation of crystals in the inner zone supports the presence of plug flow in a pseudoplastic lava the textural features of the studied lava may be related to different mechanisms i e lateral expansion we conclude that the observed crystal alignments and imbrication structures may be related to a plug flow moving between two non deforming walls the walls are represented by the solidified broken upper and basal crust of the flow the low shear strain values calculated in the outer margins of the flow are indicative of the last deformation event crystal preferred orientation and imbrication structures may be related to the occurrence of velocity gradients existing between the inner zone of the flow and its solidus or near solidus outer margins

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

carbon and oxygen isotopic records of benthic foraminifera from the northeast indian ocean implications on glacial interglacial atmospheric co2 changes abstract we present here continuous records of 18o and 13c in benthic foraminifera extending well into the last ice age in two piston cores from the andaman sea sill depth 1 3 km and the bay of bengal 3 km these show that contrary to the previous reports the glacial to interglacial shift in 13c at mid depths in the northeast indian ocean was indistinguishable from the mean oceanic 13c change negating a more vigorous renewal of intermediate waters globally during the glacial time the corresponding 13c shift in deep waters is estimated to be about 50 larger than that reported previously jointly with some recent data from the pacific our results indicate a modest glacial holocene shift in the intermediate to deep water chemical gradients in the indo pacific as a whole implying that it was perhaps not the dominant mechanism for the glacial interglacial atmospheric co2 variations also in conflict with previous work our measurements suggest significant cooling of both the intermediate and deep waters during the glacial time the high resolution records from the andaman sea help reconstruct paleoenvironmental changes at intermediate depths during the last deglaciation rapid increases in 13c occurring in two stages during the early deglaciation appear to have been caused by the fluctuations in the north atlantic deep water production a negative excursion in 13c during the mid deglaciation is ascribed to enhanced nutrient regeneration at mid depths associated with the greatly intensified summer monsoon around the pleistocene holocene boundary

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

cadmium and delta13c paleochemical ocean distributions during the stage 2 glacial maximum changes in heat and salt transport by ocean currents have been implicated in ice age climate cycles weyl 1 968 newell 1 974 broecker et al 1 990b in addition to the direct physical effects of the ocean on climate the ocean carbon system controls atmospheric co2 and the co2 fluctuations documented in ice core bubbles barnola et a1 1 987 neftel et a1 1 988 are thought to be a significant factor in climate oscillations hansen et al 1 984 dramatic changes in oceanic circulation patterns and carbon system chemistry have occurred during the late quaternary glacial interglacial global climate cycles boyle keigwin 1 982 curry lohmann 1 983 shackleton pisias 1 984 boyle keigwin 1 987 duplessy et al 1 988 curry et al 1 988 broecker et al i 990a these changes in the ocean system may be significant driving forces in the progression of ice age co2 cycles toggweiler sarmiento 1 985 ennever mcelroy 1 985 wenk siegenthaler 1 985 boyle 1 988a b broecker peng 1 990 the oceanic distributions of c513c cd and other carbon system linked properties are controlled by the interaction between biological uptake and decomposition with the general circulation of the ocean because records of past oceanic cd and c5 1 3c are preserved in shells of planktonic and benthic foraminifera

late quaternary palaeoceanography of the circumpolar deep water from the south tasman rise we use sediment cores from the south tasman rise str to reconstruct deepwater circulation in the southwest pacific sector of the southern ocean sediment cores md972106 45 09 s 146 17 e 3310 m water depth and gc34 45 06 s 147 45 e 4002 m water depth preserve records covering the last 160 k yr with chronology controlled by calibrated accelerator mass spectrometry radiocarbon dates and benthic foraminiferal 18o tied to specmap the stir benthic foraminiferal 13c records provide new 13c values for southern ocean deep water spanning the last 160 kyr at sites unlikely to be affected by variations in productivity the records establish that glacial benthic foraminifera cibicidoides spp 13c values are lower relative to interglacial values and are comparable to previous glacial benthic 13c records in the indian and pacific sectors of the southern ocean comparisons of the benthic foraminiferal 13c time series at the str are made with the equatorial pacific v19 30 and site 846 and the equatorial atlantic geob1115 the similarity of benthic 13c records at the str to the equatorial pacific suggest the southern ocean deep water mass closely tracked those of the deep pacific and the presence of a 13c gradient between the str and the equatorial atlantic suggests there was continual production of northern source deep water over the past 160 k yr

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

influence of bottom currents on the sedimentary processes at the western tip of the gulf of corinth greece abstract we investigated the sedimentary processes that were active during the holocene in the gulf of corinth using high resolution seismic reflection profiles and gravity cores seismic reflection data clearly show the presence of shallow water sediment drifts at the western end of the gulf close to the rion sill that links the gulf to the ionian sea short cores indicate that drifts are composed of homogenous bioturbated mud in their upper part the drift deposits flank a wide central area where the seafloor is eroded and where pre holocene deposits locally outcrop the seafloor morphology in this area is marked by furrows oriented in different directions and by a depression attributed to the action of bottom currents the magnetic fabric of sediment samples from the drift shelves sub basins and from the basin floor shows a significant anisotropy and a similar orientation of k max axes along core the largest anisotropy p 1 043 0 007 is observed in the drift and is interpreted as resulting from the action of bottom currents the similar orientation of k max axes in the other cores collected from areas east of the drifts suggests that bottom currents also affect sediment deposition in the rest of the study area even if seismic profiles and core analyses demonstrate that gravitational processes such as submarine landslides and turbidity currents exert the main control on sediment transport and deposition average k max axes for four cores were reoriented using the declination of the characteristic remanent magnetization k max axes show variable orientations relatively to the slope of the seafloor between along slope and roughly parallel to the contour lines

on the deformation and freezing of enclaves during magma mixing abstract mixing of an enclave of hot mafic magma into cooler silicic magma involves the competing effects of heat transfer acting to rigidify the enclave and viscous shearing imposed by a flowing host magma acting to deform and disperse the enclave we model the time required to grow a rigid chilled margin and compare this with the time required to deform the initially hot enclave whether an enclave will deform before it freezes depends on the ratio of the thermal and deformation timescales pe app 3 a 2 s r 2 and the dimensionless rigidification temperature t r t s t m t s where app is the applied shear stress a is the enclave radius is the thermal diffusivity s is the viscosity of the host r is the strength of the chilled rind t r is the temperature at which the enclave attains strength r and t m and t s are the initial temperatures of the mafic enclave and silicic host according to the model small values of pe and large values of promote rapid rigidification the model is verified by laboratory experiments on the flow and freezing of polyglycol wax droplets in cold water geological observations show that correlations between enclave size degree of deformation and local shear stress match the model s predictions studies of enclave size and shape as functions of eruption rate and position within lava flows and minor intrusions offer a new technique for studying magma flow processes during eruptions

constraints on the alkalinity and circulation of glacial circumpolar deep water from benthic foraminiferal barium the role of the ocean in driving the glacial reduction in atmospheric carbon dioxide remains an enigma several recent hypotheses have invoked a redistribution of oceanic alkalinity as a possible cause of the glacial to interglacial atmospheric pco2 change boyle 1988a b broecker and peng 1989 here i attempt to use paleo barium data derived from ba ca of benthic foraminifera to reconstruct chemical changes in glacial circumpolar deep water cpdw these new data indicate that glacial cpdw was enhanced in ba by up to 20 presumably due to the elimination of the low ba north atlantic deep water nadw flux to the southern ocean this change in ba can be used to constrain changes in cpdw alkalinity due to circulation changes alone the ba data suggest glacial cpdw alkalinity was perhaps 20 to 25 equiv kg higher than in the modern ocean following the polar alkalinity hypothesis this difference could account for about one third of the pco2 drop broecker and peng 1989 the new ba data further confirm the homogeneous deepwater distribution of ba during the last glacial maximum of the three paleochemical tracers of circulation recorded in benthic foraminifera cd ca 13c ba ca the glacial ba ca data appear to record the most marked reduction in the influence of nutrient depleted nadw in the deep oceans

hydrographic changes of the southern ocean southeast indian sector over the last 230 kyr hydrographical changes of the southern indian ocean over the last 230 kyr is reconstructed using a 17 m long sediment core md 88 770 46 01 s 96 28 e 3290m the oxygen and carbon isotopic composition of planktonic n pachyderma sinistra and g bulloides and benthic cibicidoides wuellerstorfi epistominella exigua and melonis barleeanum foraminifera have been analysed changes in sea surface temperatures sst are calculated using diatom and foraminiferal transfer functions a new core top calibration for the southern ocean allows an extension of the method developed in the north atlantic to estimate paleosalinities duplessy et al 1991 the age scale is built using accelerator mass spectrometry ams 14c dating of n pachyderma s for the last 35 kyr and an astronomical age scale beyond changes in surface temperature and salinity clearly lead by 3 to 7 kyr deep water variations thus changes in deep water circulation are not the cause of the early response of the surface southern ocean to climatic changes we suggest that the early warming and cooling of the southern ocean result from at least two processes acting in different orbital bands and latitudes 1 seasonality modulated by obliquity affects the high latitude ocean surface albedo sea ice coverage and heat transfer to and from the atmosphere 2 low latitude insolation modulated by precession influences directly the atmosphere dynamic and related precipitation evaporation changes which may significantly change heat transfer to the high southern latitudes through their control on latitudinal distribution of the major frontal zones and on the conditions of intermediate and deep water formation

on the origins of deep and bottom waters of the indian ocean the characteristics of the deep and bottom waters of the indian ocean when illustrated on potential density anomaly surfaces indicate that the waters enter from both the atlantic and pacific oceans the paths of spreading are constrained by the complex topography and characteristics are seen to be altered by exchange with the overlying and underlying water and with the sediments especially in the northern indian ocean the weddell sea contributes to the densest waters found in the western basins and the ross sea and adelie coast to the densest waters found in the eastern basins both dense water varieties are altered by and incorporated in the less dense water above initially water carried by the circumpolar current then water from the north atlantic and finally by deep water whose characteristics are derived in the northern indian ocean contact with the sediments increases the silica content of the bottom water in the southern ocean in the northern indian ocean the sediments alter the silica of the water at the bottom and together with enhanced salinity from diffusion of saline overflows from the marginal seas above imprint unique markers to the deep water that flows back to the south at middepths the series of ridges between madagascar and australia confine the flow to a series of gyres that carry characteristics from the circumpolar current equatorward and the northern indian ocean characteristics southward within the circumpolar current low oxygen deep water from the pacific is carried across the atlantic and into the indian ocean south of africa part flows around the cyclonic weddell sea gyre and part extends across the southern ocean water from another pacific source can be seen near 2000 m extending westward from the tasman sea south of aus tralia and across the indian ocean and perhaps to the aghulas current region southeast of africa in this study we show some maps of deep and bottom water characteristics of the indian ocean which may be used in a qualitative sense to infer pathways of spreading of water below a depth of about 2000 m the indian ocean has numerous ridges and basins figure 1 that severely restrict possible pathways of deep and bottom wa ter flow in the following we will begin by looking at char acteristics at the bottom of the ocean to reveal the path ways of spreading of the densest bottom waters from basin to basin then a series of six potential density anomaly surfaces at progressively shallower depths from about 4000 m up to about 2000 m will be shown to see what character istics influence the deep waters and how pathways of flow are constrained by the bathymetry of the indian ocean the choice of the specific density levels table 1 was based primarily on various property extrema shown by the 18os atlantis ii cruise 93 colored sections that accompany warren s 1981 detailed discussion of the major features of the central indian ocean between madagascar and aus tralia the sections approximately midway between antarctica and the northern indian ocean boundaries are well positioned to show features originating from both the north and the south as well as some brought into the indi an ocean by the antarctic circumpolar current the full ocean area isopycnal maps provide essential evidence on the origins and fates of features seen in the sections and

the significance of microgranitoid enclave shapes and orientations abstract enclaves are often incorrectly used to measure magmatic strains in plutons we emphasize that microgranitoid enclaves are not like other ellipsoidal markers used to determine strain for the following reasons 1 adjacent enclaves may form at different times and different places and initially have non spherical shapes with axial ratios up to 2 7 2 the final shapes and orientations of enclaves are a complex function of a initial shape and temperature of enclaves b subtle changes in composition melt percents volatiles grain sizes and thus temporally variable viscosity contrasts between the enclave and magma c a competition between strain and interfacial energies and d deformation path which may include internal strain and rigid rotations caused by magma flow during ascent convection expansion chamber boundary processes and tectonism 3 enclaves spend much of their time in magma as relatively rigid objects and thus rigidly rotate and potentially break apart rather than strain at matrix strain rates 4 in some instances enclaves do not record or track finite strain because of the above final enclave populations are heterogeneous and the use of single enclaves or enclave populations as strain markers violates many assumptions needed to complete strain analyses on the other hand a comparison of the preserved characteristics of igneous layering mineral fabrics and carefully evaluated enclave fabrics including internal mineral alignment in enclaves may provide qualitative data on the changing magnitude and kinematics of magmatic strains

experimental and textural constraints on mafic enclave formation in volcanic rocks abstract we have used experiments and textural analysis to investigate the process of enclave formation during magma mixing at southwest trident volcano alaska andesite enclaves are present throughout the four dacite lava flows produced by the eruption and resemble mafic enclaves commonly found in other volcanic rocks our experiments replicate the pressure temperature time path taken by enclave forming andesite magma as it is engulfed in dacite during magma mixing pressure and temperature information for the andesite and dacite are from coombs et al contrib mineral petrol 140 2000 99 118 the andesite was annealed at 1000 c and then cooled to 890 c at rates of 110 c h 1 10 c h 1 and 2 c h 1 once cooled to 890 c andesite was held at this lower temperature from times ranging from 1 to 40 h the andesite that was cooled at the slower rates of 2 c h 1 and 10 c h 1 most resembles enclave groundmass texturally and compositionally based on simple thermal calculations these rates are more consistent with cooling of the andesite groundmass below an andesite dacite interface than with cooling of enclave sized spheres if enclaves do crystallize as spheres post crystallization disaggregation must occur calculations using the melts algorithm ghiorso and sack contrib mineral petrol 119 1995 197 212 show that for incoming andesite to become less dense than the dacite 34 volume of its groundmass must crystallize to undergo 18 volume vesiculation these values are similar to those determined for southwest trident enclaves thus such crystallization may lead to flotation of enclaves and be a viable mechanism for enclave formation and dispersal the residual melt in the cooling experiments did not evolve to rhyolitic compositions such as seen in natural enclaves due to a lack of a decompression step in the experiments decompression experiments on southwest trident dacite suggest an average ascent rate for the eruption of 2 3 mpa h 1 an andesite experiment that was cooled and then decompressed at this rate contains melt that matches that of the natural enclaves it is apparent that decompression ascent induced crystallization occurs in enclaves but not in the form of microlites as happens in the dacite host due either to insufficient residence time at chamber temperatures or to the pre existing microphenocrysts which act as sites for new growth

oceanic oxygen 18 at the present day and lgm equilibrium simulations with a coupled climate model of intermediate complexity abstract an earth system model of intermediate complexity climber 2 is used to simulate the oxygen 18 content of the water masses h182o in the oceans firstly we forced climber 2 with the fluxes from the atmospheric general circulation model echam simulated oceanic 18o fields for the present day are in good agreement with data secondly a water isotope module was developed to transport 18o in the atmosphere on a large scale and compute the 18o fluxes to the ocean at the atmosphere ocean interface using only variables already computed by climber 2 for the present day we successfully represent oxygen 18 distribution in the atlantic indian and pacific oceans and close agreement is also found when we compare modelled and observed 18ow salinity relationships during the last glacial maximum lgm we find that the major differences in the 18o oceanic fields apart from the global oceanic enrichment due to ice sheet build up are due to surface condition changes surface temperature shift in bottom water formation zones and that no drastic changes occurred in the 18ow salinity spatial relationship in addition we compute a calcite 18oc field for the atlantic and compare it to the available data to assess the variation between the lgm and the present day

evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate evidence from southern ocean sediments for the effect of north atlantic deep water flux on climate

microhabitat preferences and stable carbon isotopes of endobenthic foraminifera clue to quantitative reconstruction of oceanic new production seventeen surface sediment samples from the north atlantic ocean off ne greenland between 76 and 81 n and nine samples from the south atlantic ocean close to bouvet island between 48 and 55 s were taken with the aid of a multiple corer and investigated for their live rose bengal stained benthic foraminiferal content within the upper 15 cm of sediment preferentially endobenthic melonis barleeanum m zaandami and bulimina aculeata as well as preferentially epibenthic lobatula lobatula were counted from 1 cm thick sediment slices each and analyzed for stable carbon and oxygen isotopic compositions of their calcareous tests live and dead specimens were counted and measured separately the carbon isotopic composition of the foraminifera was compared to that of the dissolved inorganic carbon dic of simultaneously sampled bottom water during a period of one month one station off ne greenland was replicately sampled once every week and samples were processed as above live specimens of lobatula lobatula are confined to the uppermost two centimeters of sediment live specimens of melonis spp are found down to eight centimeters within the sediment but with a distinct sub surface maximum between two and five centimeters the down core distribution of live bulimina aculeata shows a distinct surface maximum in the top centimeter and constant but low numbers down to 11 cm subbottom depth the average stable carbon isotopic composition d13c per mil vpdb of live l lobatula off ne greenland is by 0 4 0 1 per mil higher than the d13cdic of the ambient bottom water at the time of sampling there is evidence that this species calcify before the ice free season when bottom water d13cdic is supposed to be higher this would reconfirm the one to one relationship between d13c of ambient water dic and cibicids widely used by paleoceanographers live m barleeanum show a negative offset from bottom water dic of 1 7 0 6 per mil in the uppermost sediment and of 2 2 0 5 per mil in three to four centimeters subbottom depth all d13c values of live melonis spp decrease within the upper four centimeters regardless of the time of sampling and site investigated the offset of live b aculeata from bottom water d13cdic values of eight stations rather constantly amounts 0 6 0 1 per mil no matter what subbottom depth the specimens are from at one station however where is strong indication of elevated organic carbon flux the negative offset averaged over all sub bottom depths increases to 1 5 0 2 per mil buliminids actively move within the sediment and by this either record an average isotope signal of the pore water or the signal of one specific calcification depth the recorded signal however depends on the organic carbon flux and reflects general but site specific pore water d13cdic values if compared with epibenthic d13c values from the same site not influenced by pore water and related phytodetritus layer effects bulimina d13c values bear some potential as a paleoproductivity proxy specimens of melonis spp seem to prefer a more static way of life and calcify at different but individually fix depths within the sediment although live specimens thus record a stratified pore water d13c signal there is no means yet to correct for bioturbational and early diagenetic effects in fossil faunas